Actually, anything can be compared (for "compare" means similarity and difference). Wikipedia is full of original research, despite its conflicting/contradicting policies about it (and many other things).
The Dev Master, Game Programming, and other game development wikis don't need to waste articles explaining concepts when Wikipedia does a far better job. Instead, such topic-specific wikis can focus on "how-to" tutorials/guides, unreferenced original research, and deleted content from Wikipedia that is still relevant (like my "action (gaming)" article, despite having sources).
I'm experimenting with a wiki for my 3D Game Comparison and it will link extensively to Wikipedia for general info about games, companies, game features, etc (as the non-wiki site currently does). However, site-specific "articles" (more like categories and the comparison table) can stay on my separate wiki (for now; I'd rather have a single wiki for everything--including dictionary entries--but WikiMedia doesn't agree, unfortunately). I'm going to try using the Semantic MediaWiki extension (which isn't installed on Wikipedia, as far as I can tell) to get a more database-like system that auto-generates tables without actually having to deal with database design (at least as far as I understand what a semantic wiki is thus far--having only been exposed to it for a few hours now).