Nintendo's Virtual Console is a great way to catch up on old games from a variety of developers and systems, Sony has been releasing PS1 classics since soon after the launch of the PS3, and Microsoft's Xbox 360 has played host to old gems like Banjo Kazooie and Castlevania: Symphony of the Night. Having all the old games you love on your current console has a lot of appeal and while some developers seem to be milking their franchises a bit (I'm looking at you Square Enix with your countless Final Fantasy 4 remakes), I find it hard to turn down an updated classic. It's the equivalent of the film industry releasing classics on Bluray.
I've got to say that I'm glad it's so easy to pick up old games and relive the days of Super Mario World or Final Fantasy 7 without worrying about multiple discs or blowing dust out of a cartridge. Heck, I can even pick up classic console games and play them on my handhelds!