the 360 is working to the limits of its potential now, but the ps3 is working at about half capacity, leaving loads of room for improvments.
the 360 has a failure rate of about 20% now and the ps3 is well under 1%. (360 fanboys need to ask yourself how many 360's have you already gone through???)
ps3 comes with everything built in!! 360 is all just expensive add-ons.
new games that want to hold massive amounts of game data to make their titles better and better can only do it on the ps3... take mgs 4 for instance, the 360 would have to graphically dumb down and cut a major amount of the game out to get them on the discs.
the list goes on and on, like online gaming... the 360 is slightly better but when you dont have to pay for it then you dont really care to much about the difference.