No... The Xbox 360 install is 3.8 gb, Now the PS3 is 5.5 gb (required install) as its Blu Ray drive reads slowly so a bigger install makes sense.
This has nothing to do with BluRay drive speed.
It would make sense, if both were partial installs and the one from the PS3 is larger to overcome the slow drive speed and the Xbox drive is fast enough to install less.
But that's not the case.
The install on the Xbox360 is 3.8GB for the full game, the 5.5 on the PS3 is only a partial install, not the full game.
The game is for whatever reasons vastly larger on the PS3 which is normally a very good sign for the PS3 version.