I've always found those things fascinating but in answer to your question, no I don't know of any sites devoted solely to that. My first port of call is usually a message board, say, GameFAQs, where there's usually a million threads asking 'what's the difference'. Hardcore Gaming 101 usually also does a good job of getting into all those things, but its not like they cover a lot of games or franchises in the grand scheme of things and not as though many of them are new / current.