Spelunky is amazing. I love it a bunch.
But yeah, the 360 version is apparently supposed to be pretty different. He doesn't want to make a port or anything, and I think he wants to make it different since Spelunky for PC is already there, free, and Spelunky for 360 will cost money.
I read something like that from the guy, at least. I forget his exact words.
But yeah, awesome game. Haven't beat it yet, but yeah.