Hulu says that it’s “free online video service that offers hit TV shows including Family Guy, 30 Rock, and the Daily Show with Jon Stewart, etc.” Unless, though, you own a Sony PlayStation 3. If that’s you, you’re out of luck.

PS3 users discovered starting over the June 27th weekend that when they tried to watch a video that instead of their TV show or movie, they got the annoying message: “Unfortunately, this video is not available on your platform. We apologize for any inconvenience.” That didn’t go over so well with PS3 users.

What’s happening is that when the PS3 Web browser tries to pull video content down from Hulu it first sends its User Agent String. All Web browsers send these strings when they connect to a site. They usually are made up of the application’s code name, it’s regular name and version number, it’s operating system (Linux, Windows, etc.) and the browser’s creator.

In the case of PS3, the User Agent String is “Mozilla/5.0 (PLAYSTATION 3; 2.00).” When Hulu gets the string, whether it’s sent from a PS3 or from a Web browser pretending to be a PS3, it won’t send the video.

While I’m not a PS3 user, if there’s a way to reset that string, as there is in Firefox on Linux, Mac OS, and Windows, to another User Agent String, it should be possible to dodge Hulu’s restrictions… for now. There are other, more difficult to implement, ways to block users of course.

PS3 users may only be the first to face this problem. When Hulu updated its Terms of Use, it did not state that it was going to block PS3 users. It did, however, say that “Hulu is pleased to grant you a non-exclusive limited license to use the Hulu Services, including accessing and viewing the Content on a streaming-only basis through the Video Player.”

The Video Player is almost certainly what Hulu has been calling the Hulu Desktop. This is a video program that works on Windows and Mac systems. Could it be that Hulu is planning on forcing all its users to sticking with this program? I’d bet on it.

Why? Because Hulu owns 10% of the online video market. That market, according to a report from Screen Digest, was worth $448-million in 2008.

Hulu, and its owners, wants more control over that money. Hulu has long been fighting with Boxee‘s developers to keep the popular video extender program users from viewing Hulu-based content. Blocking PS3 users was just the natural next step. I am completely certain that by summer”s Hulu will be blocking anyone who doesn’t use the Hulu Desktop and the Hulu controlled advertisements and revenue that goes with it.