User blog comment:SilverPlays97/Sonic the Radioactive Hedgehog/@comment-477304-20130117202705/@comment-115265-20130125061828

Yes, I agree. Though my own head-canon (as in, what I believe the canon to be), indicates Sonic and friends simply... aged.

I have a lot of trouble believing radiation and stuff is what caused any change in appearance. But hey, that's the name of my game.