i think in My Opinion that's it's the market of each system, if you look at what each system is designed from the get go they are not quite the same.
i think it just boil's down to the market for both being:
the PS3 is more of a MULTI-MEDIA system "that play's game's"
and the XBOX360 is more of Game's machine "that play's multimedia"
that play's part is what i think that make's each targeted toward their main market.
which is why if your more of a "gamer" type person than if you like to watch more movies, or use the system for more non game related function's.
you would be more inclined to choose the xbox360 and or the Wii over the PS3. this is not a slight against the PS3 as "not being a game's machine" because I think its a very good game's machine.
I just think that Sony's machine is made more for Multi-Media function as a "more all arround entertainment machine" I think if you notice, folding@home, linux install,playstation life, home. those are function's that are shall we say NOT of the highest "priority of gamer's list of function's" for the most part, Now that's my Opinion that it's not but i think it's a sound one.
People may consider that Sony has gone in the wrong direction, but that may be for you but not for other's. I Happen to like the direction of the PS3,but that also mean's i may not be as much of a hardcore "gamer" as i used to be. i happen to use my PS3 for quite a number of thing's that are non gamer related.I see the PS3 as more of an evolution of the direction that the first playstation was designed arround. more of a all arround Entertainment device than targeted toward one part of Entertainment.
I think that in of it self may have something to do with it.
Two seperate consumer market's within their consumer base that buy's each system.