Yep, the Show is a PS3 exclusive. I haven't played MLB2K since 2007 because I've been with the Show since then, but I've heard nothing but bad things about it since 2009. Game is apparently full of bugs and glitches and isn't a good baseball game. It's been bad enough that 2K felt like they couldn't compete with the Show anymore and have decided to quit making the game. The Show will be the only baseball game on the market this coming year.
But I see no harm in getting 2k12 for about $30 now just to see if you might enjoy it. One of my friends seems to enjoy it, so it's probably hit or miss with some people.