I'm not really big on Tekken, but with the pretty hefty number of games switching from Sony exclusive to multi platform in the last I dunno, however long the systems have been out...
...Well, I don't think we should get too worked up about it. I mean, come on. Final Fantasy is porting to 360. It's hard to get mad about Tekken doing it.
A game goes "multiplatform" because the company making it expects a nice profit. And you'd make more money selling it to all the major platforms than just being exclusive to one. The downside is the amount of time/money spent on developing for other platforms. That's how I see it anyway...
For those who really like 360/PS3 comparisons, check out Lens of Truth
I'm sure they'll eventually get around to a detailed comparison between Tekken 6 versions.
EDIT: Scratch that, they did.
It looks like loads times made those guys choose the 360 version over the PS3 version, but they did bring up the PS3's antialiasing.
I find their evauations based on load times a bit sketchy. They admitted they were biased against installs, but with the video comparing the load times between the 360 and the PS3 with the game installed, they looked identical. The only difference I saw was they started the video a split second behind on the PS3. So, if you're willing to install it, then it looks like the choice should be the PS3. I've noticed in their reviews, though, they never take the installed version into account when evaluating based on load times. They did the same thing on the Street Fighter 4 review where they said the 360 won out on load times even though the PS3 loaded faster with the install. Installs aren't so aggravating to me that I can't stand a one-time install when you first start up a game. Hell, most games these days bug you about installing an update first thing, so waiting to play a game is becoming commonplace on all systems.