Ok, it's really not. There have been Terry Trickett's Air Friday and more recently, we made a special one for Gregg Patberg with an adjustable rear brake mount.
That one ended up in the hands of one Billy Fenton who sent me a picture. The bike actually was sort of an experiment to see if we could make a production fixed gear but I believe the adjustable rear brake mount ended up killing it.
When I did mine (see here and here and a little pic here) I had already put together a big wheel fixie (read the story and check out the new and old pics) and realized I didn't need any more than a front brake (now I'm not running any.. before you freak out read) so I didn't need this.
And incidentially my bike became an inspiration to run a production run of them. I'm happy to accounce that the first official fixed gear Pocket Rocket has been delivered and is currently being enjoyed by one Joel Young. He's got a nice blog which includes a great ride report and some nice pictures, too.
So if you, too, want to get fixed, let me know. And if you want to know why, I'd be glad to tell you, but you might check out: