Joker DLC I would argue is probably the main reason.  It is why I got it on the PS3 instead of the 360.

Street Fighter, Resident Evil 5, Batman AA, blazblue calamity trigger, FIFA, PES,bayanetta, and a lot of other games outsold their 360 counterpart so this is not anything new. The question you should be asking is whether those who bought the 360 version also "double dipped' and bought the ps3 version as well. That really is the "bigger" question.

^nah, the big thing here is : those games aren't shooters.

Arkham Asylum overrated? Some of you need to take lithium pills.

Batman AA is a solid 8.6 in my book, a little tiny bit overrated by some "reviewers", but that's come to be expected these days (Halos, GTAs, COD MWs, Mass Effects, etcetera, etcetera, etcetera)

It was the joker. I have 360 and despite the demo being great I didn't buy it out of spite for the joker being exclusive. I am not going to pay the same price and get what I perceive to be significantly less content.

This should explain the rather obscure meme. (urbandictionary)

2. Sea Turtles 6 up, 1 down
When something inexplicable happens, or you don't want to explain something, you can use "Sea Turtles" as a stand in.
'Teague beckons forth the dog with the keys, last left on the cannibal island'
Ragetti: Is that... can't be.
Pintel: How?
Captain Teague: Sea turtles, mate.

And baby seals?

Fifa,PES,Tekken,DBZ,Batman...many games on ps3 better, i think. And yes, the batman ps3 game have joker, this is awesome

Something DollaDolla started I believe. When someone would use Amazon as a sales source, he said someone was clubbing a baby seal.