Not even Sookie Stackhouse's mysterious fairy abilities or Eric Northman's vampire strength are powerful enough to keep HBO's subscriber base from seeping away.

As a feature in today's Hollywood Reporter notes, the cable network is just coming off a hit season of 'True Blood' (which wrapped with a third-season finale last night) and its usual domination of the Emmys, led by its prize-winning marquee mini-series 'The Pacific.' And yet its subscriber base has slipped to 28.6 million, its lowest total in four years, suffering two quarterly periods of back-to-back slippage for the first time in six years.

The Reporter speculates on several possible reasons for the decline, from the economy to increased competition from other premium cable channels to the morphing business model of the cable industry. But the article downplays what is perhaps the simplest explanation: maybe HBO's programming just isn't as compelling as it was in the days of 'The Sopranos' and 'Sex and the City.'

It's certainly reasonable that recent upheavals in both the economy and the cable business would lead some HBO viewers to drop their subscriptions. Many viewers have been hard hit by the current economic crisis, making premium cable a luxury they're no longer willing to pay for.

There's also been increased competition from such premium channels as Showtime and Starz, both of which have rolled out original programming that rivals HBO shows in dramatic intensity, quality writing, and luridness. (Both channels have seen steady subscriber increases over the last six years, though they're still both below 20 million, well below HBO's numbers.)

As for changes in the nature of the cable business, the Reporter suggests that HBO may be a victim of its own success in finding alternate revenue streams. DVD sales of HBO series comprise as much as 15 percent of the channel's revenue -- including a reported $100 million to date for 'True Blood' discs. But now that fans know they can catch a full season of that show, or 'Hung,' or 'Entourage,' within a few months of its air date on DVD or iTunes, there's less incentive to subscribe.

And HBO may also be falling victim to the carriage-fee wars between programmers and service providers. In recent months, several basic-cable channels and their parent companies (including such powerhouses as Disney and News Corp.) have tried to make up diminished ad revenue by squeezing cable and satellite providers for increased carriage fees by threatening -- and, in some cases, making good on threats -- to yank their signals from millions of homes.

According to the Reporter, the service providers have now figured out a way to fight back, at least against premium subscription channels: by withholding promotional support. If, while you're watching the guide scroll, you're not seeing promos for HBO's shows, you may be less likely to maintain your subscription. Both DirecTV and Comcast have been squeezing HBO with this tactic, according to the Reporter, which lays most of the blame for HBO's woes at the feet of the satellite provider.

Of course, the cable business as a whole remains so volatile that a 5 percent drop in subscribers is par for the course for any premium channel at any time. According to the study by media research firm SNL Kagan that the Reporter cites, the whole industry lost subscribers in the second quarter of 2010, marking the first quarterly loss ever for the entire cable and satellite subscriber base.

It's not because of outside competition from video content on the Internet, the firm says; rather, it's the slow economy and the expiration of promotional deals that lured new customers to cable and dish providers last summer when the digital broadcast signal conversion took place.

Still, there's the simplest but most glaring possible explanation is that the shows are just not as compelling any more. 'True Blood' is a frequently great show, but critics like TV Squad's Maureen Ryan have complained that the third season, with its all-over-the-place plotting, seemed to have lost the focus and emotional impact of seasons 1 and 2.

Coach-turned-gigolo comedy 'Hung' has a clever premise and offers often incisive observations on class and gender amid the current economic malaise, but not much happens on the show, which has been frustratingly hit-or-miss during its second season (which also concluded last night).

And 'Entourage' (which marked yet another of last night's HBO season finales) has been on the downswing for a long time, and news that the next season will be just six episodes long suggests that it's only hanging on long enough to tie up the plot's loose ends.

HBO's award-winning mini-series and original movie programming may be stronger, judging by the Emmy cleanups for 'The Pacific,' 'Temple Grandin,' and 'You Don't Know Jack.' Still, 'The Pacific' didn't have anything like the cultural impact of its predecessor, 'Band of Brothers,' a decade ago, and it's likely most people heard about 'Temple Grandin' and 'You Don't Know Jack' for the first time at the Emmys.

The Reporter is dismissive of the notion that show quality has a direct correlation with subscriptions, noting that HBO viewership actually rose a little bit for each of the four quarters following the departure of the 'Sopranos,' reaching a peak of 29.1 million in early 2009. "Maybe the 'Sopranos' magic just took a long time to wear off," the article says.

Well, actually, yes. The hype around the 'Sopranos' finale in 2007 was so pervasive that it probably drew new subscribers who just wanted to see what all the fuss was about. Also, during those four quarters, viewers could see such shows as 'Big Love,' 'Curb Your Enthusiasm,' and the not-yet-peaked 'Entourage,' as well as more cultish but acclaimed shows like 'The Wire' and 'Flight of the Conchords.'

Even today, 'The Sopranos' and 'Sex and the City' (which left the air in 2004) remain so central to HBO's brand identity that you can still watch old episodes of both on HBO's on-demand service. Think viewers will still be queuing up episodes of 'Hung' or 'Entourage' in six years?

It's worth noting that HBO's co-president Eric Kessler professes not to be worried by the two consecutive quarters of declining subscribers. "This kind of fluctuation is common throughout the year," Kessler said in a statement. "The most important measurement of success is financial and HBO will enjoy another record year in revenue and profit."

It's also worth noting that HBO has had no decline in the ambition of its programmers, as evidenced by such lavish upcoming shows as crime drama 'Boardwalk Empire' (which debuts next week) and 2011's fantasy series 'Game of Thrones.' The TV press has already been talking about 'Boardwalk Empire' like it's the next 'Sopranos' (to which it has some family ties: writer/producer Terence Winter, star Steve Buscemi, and a New Jersey setting).

And maybe it is, but such talk proves HBO still does one thing well: stir up buzz among TV critics who, like the network's executives, hope the next show will be the one that returns HBO to its glory days.


•Follow Gary Susman on Twitter @garysusman.