It's obvious FPS are popular on xbox and this board is more active.
if you check fighting games you will see that xbox people are on ps3 board. --- PSN/Battlelog: tactikz4 BF3 Best Multiplayer join platoon: http://battlelog.battlefield.com/bf3/platoon/2832655241111991065/
I own both consoles but use my PS3 for the majority of my online gaming. And yeah, the 360 boards are almost always more active, (especially for FPS). I also owned a 360 first so I am used to posting on these boards.