Sales later this year will be dependent on how Sony's Arc and Microsoft's Natal performs, games won't be the major selling point for hardware later this year the motion controls will mark my words, this is what both console makers are focusing on for the last half of the year.
If Natal lives up to the hype I really can see the 360's sales going off the scale, the hype surrounding Natal is already huge and will only get bigger after E3, Sony's Arc has a LOT to live up to as at the moment it just looks like a wii mote copy.
I expect the gap to get even larger (in 360's favour) and maybe the biggest it has ever been by this time next year, this is IF Microsoft gets Natal right on price, game support and marketing.
Oh, and don't forget Halo: Reach, this WILL be the biggest exclusive game this year, the recent gameplay video looks amazing and the hype around it is fantastic and it is HALO!