BOSTON (CNN/Money) - What does $90 billion buy you these days? Not as much as you thought it would eight years ago.

That's probably what most cable-company CEOs are thinking as 2004 winds down and they calculate what they got for the corporate treasure they spent to upgrade their networks after the 1996 Telecommunications Act.

Sure, they got the digital upgrades, which gave them the ability to offer that sweet trifecta of voice, video, and data. And the DVR craze sweeping through the United States, which satellite providers jumped on, plugs and plays nicely now on the digital networks.

But what was thought to be the keystone of the effort -- video-on-demand -- has yet to provide the kind of revenue and customer retention that companies had predicted back in the late 1990s. (Remember Qwest's "any movie at any time in any language you want" ads?)

Last week, Comcast CEO Brian Roberts gave attendees at Merrill Lynch's Media and Entertainment Conference some tantalizing news on the growing popularity of VOD, four years after the first VOD rollouts. Sixty percent of Comcast's 21.5 million subscribers are now VOD-ready, and in July those customers downloaded 50 million shows, up from 40 million in June. That's almost a movie a week for each customer.

Pretty healthy growth, to be sure, and it was good news for the company's stock, which had been hovering near the 52-week low it set in August. Investors pushed the stock up more than 2 percent on Wednesday.

But investors shouldn't get too ecstatic. For one thing, in his speech, Roberts mentioned that 15 million of the 50 million shows downloaded in July were programs from HBO. He touted the figure as proof that people don't want to watch programming on the networks' schedule.

But those 15 million shows were downloaded at no extra cost to the customers; digital HBO subscribers receive access to select HBO VOD content. In other words, Comcast didn't make a penny of additional revenue from those downloads.

"If you look at VOD numbers overall," says Mike Paxton, a senior analyst with InStat/MDR, "most users are generally satisfied with VOD, but they're not paying in large numbers to get additional content."

VOD could help cable differentiate itself from its mortal enemies, the satellite-dish companies. Satellite providers can't offer VOD, and cable companies need to continue to hammer at Hollywood to score the kinds of content deals that will encourage people to stay with cable.

But so far, signing quality (and quantity) content remains an elusive goal for Comcast and the other cable operators.

"Comcast is still struggling with [Hollywood over] release windows," says Daniel Ernst, an analyst with Soleil Securities. "By the time it comes out on VOD, people have already seen it on DVD."

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Satellite companies are adding subscribers at a rapid pace, something the cable industry can't claim.

"Cable is not really growing at all," Paxton says. "It's seeing roughly 15 to 20 percent growth in terms of upgrades to digital cable, but net total growth for the industry will probably be down 2 to 3 percent in 2004."

For Comcast to make VOD the engine of its digital efforts, it must obtain the kind of content that will make people want to sign up for digital cable instead of satellite TV.

Netflix's growth shows, among other things, that people value convenience. VOD trumps Netflix's convenience factor, but falls behind in content.

If Roberts can square those two factors -- content and convenience -- he might have some solid numbers to trot out a year from now.

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