A few things.
1. They wont have a headstart this time out. We know PS4 is out this Year.
2. The PS4 is built by developers, for developers. This added in with the amazing specs pretty much means the PS4 wont be getting poor, gimped ports... Something that held back the PS3 and gave the 360 a great advantage for 2 Years.
3. Sony will be launching with a network that is arguably equal to Microsofts, wheras last time PSN was in all fairness rubbish.
4. Sony are now friendly with Activision. Diablo 3 on PS3 and 360. Exclusive content for Bungie's new game, Destiny... Could Call of Duty be next? We know how much Microsoft have relied on the shooter market with the 360, Sony muscling in on that could cause problems.
5. No longer having the advantage of Kinect. Sure, Kinect is the bigger and more popular product... But now the competition has something comparable. The differences could be Sony using it with controllers (DS4, Move), and of course whatever Microsoft upgrade on Kinect.
On the other hand... There a bunch of stuff that Microsoft wont care about in the slightest.
