The latest developments with streamed video via subscription highlight the weakness of the model: the lack of titles people actually want to watch.

Yesterday , giving members the ability to stream over 5,000 movie and TV show titles. Hot on the heels of that story, today Netflix worked out a deal to stream a big portion of the CBS library of TV shows on its service. Looking at what the two developments involve, you'll notice a similar pattern: in both cases, the vast majority of the content is very old.

The news about video coming to Amazon Prime was initially exciting since the service (which most people had probably dismissed because it really only offered getting your Amazon junk delivered a day or two sooner) costs less per month than Netflix, and even Hulu Plus. Now people have a reason to give Amazon Prime a second look.

If you do, though, you'll wonder why you bothered. As exciting as it may be to have another video-streaming service to subscribe to, Amazon Prime Instant Videos suffer from the same problem as other subscription-based video services: selection, or rather the lack thereof.

First of all, the offerings on Prime Instant Videos are a mere subset of what's on tap from Amazon. If you own one of the over 200 devices (TVs, Blu-ray players, and set-top boxes) that can access the Amazon video widget, you probably already know that you can watch movies and even recent episodes from many TV series—in HD—from the service (for an a la carte fee, of course). In total, Amazon offers 90,000 titles for streaming, according to a rep, which makes the 5,000 Prime videos feel not-so-prime.

Then there's the issue of what Amazon considers a "title." It turns out every single episode of a TV series counts as a title. So looking at, say, "24," which had eight seasons with 24 episodes each, that counts as 192 titles. When you start racking up whole TV seasons, you hit the 5,000 mark pretty quickly.

Finally, which titles are actually on offer? A cursory look shows movies like Risky Business, Best in Show, The Mask, Starman, Roger & Me, and Enter the Dragon. And those are just the recognizable ones—mining even further there are plenty of unknown straight-to-video flicks there, too. For TV, Amazon features "Doctor Who" Season 4, "Farscape" Season 1 (nice to know they're nerds, too), and "Nova." Titles from the past two years (movie or TV) are few. It seems Amazon equates Prime members with people who wandered aimlessly into a video store on a whim. A market, surely, but hardly a "prime" one.

I'm sort of singling out Amazon a little too much here. Even putting the CBS deal aside, if you browse the titles that Netflix offers for streaming, you'll find that many of the movies and TV shows from the last couple of years—the ones you probably really want to watch—are available only on disc.

All of this serves to underscore the weakness of the video-streaming model. While technology has improved greatly in the last few years—an HD episode of "24" that I streamed recently from Amazon looked good and crisp and didn't have any buffering problems—the selection of media you get via subscription hasn't. Hulu is kind of the exception that proves the rule, but its offerings have been curtailed since its launch in 2008—savagely, if you look at what's available on devices outside of PCs.

Will we ever see a video subscription service that actually serves up recent, top-quality titles? Maybe, though studios would want you to pay for the privilege, and my guess would be the bill would end up somewhere in the neighborhood of what your monthly cable bill costs (just for TV, not you voice or Internet). To make room for such premium content, I could see services like Amazon offering a different "tier" for the better selection of titles ("Prime" and "Really Prime"?).

And there lies the problem. Once a monthly subscription rate goes above about $15 a month, it just starts to look too damn high, no matter what's on offer. Presumably the bean counters in Hollywood have done that math, too, and have concluded that they the a la carte model makes them more money.

But we could both be wrong. Maybe the volume of customers would make the model sustainable at somewhere close to $15. My advice to any intrepid studios mulling a subscription model that includes recent titles: don't knock it till you try it.