Well, in most cases in the past, the 360 version of the multiplatform game was 720P, while the Ps3 version was less. Two big examples I can think of is Bioshock (1) and GTA4. But it was the case in many games.
It's just people ignored that, swept it under the rug, and didn't keep bumping the thread like this one will be forever, because well, fanboyism.
It was probably just a quick and bad port by SE, I guess. It's really weird though, since in the past the 360 could always handle any Ps3 port with ease, while PS3 struggled with 360 ports. Bayonetta is one example that actually gained some publicity, but there were many.
Well, if a second title comes out better on Ps3, maybe we'll have a trend lol. I doubt it though.