4gb is already a pretty small amount, by today's standards. just look at last/current gen consoles; limited RAM is a huge bottleneck. especially if all these next-gen games are going to have open-world emphasis, then that's going to start biting pretty soon. basically these consoles are going to be dated in a year or two already; and for what, fucking Kinect and fancy overlays? so I can understand it (even though it's not exactly surprisingthe OS was obviously going to use some RAM).
just look at the current generation of consoles. Epic singlehandedly got MS to double the RAM in the 360 in order to get Gears of War to run on it. New Vegas (the town) is broken up into like 5 shitty, tiny segments because of console RAM limitations, etc.