Well, that's why it's going to take a very long time to get real radiosity in a game. My idea was basicly a hack to get "radiosity-like" effects without a big performance hit, but obviously it's not implimented the same way at all. Until an engine can acurately bounce light off of every surface, with it's reflection amount and color changed depending on the material, we won't see "true" radiosity. But in the same way, games like Splinter Cell didn't have "true" shadows either. Most of the time the engine only kept track of where the light DIDN'T shine, not where it DID shine, and my idea is basicly the same thing except for radiosity instead of shadows.
Oh, and here, for an example of what I'm talking about, I rendered this scene quick using one of the random Lightwave models I made a while ago. These two scenes are identical, EXCEPT that in the right one I added 3 negative lights by the model (actually I was a bit inefficient, I could've only used 2 for almost the same effect). Now it may not be real radiosity by any means, but you gotta admit that for such a small change it does a pretty nice job of faking one of the effects that radiosity has on shadows.