Interesting theory about Grand Theft Auto 5, though they've always had a closer relationship with Microsoft then Sony. Perhaps it is the opposite, perhaps they delayed GTA 5 in order to produce an upconvert version as a launch title for the next xbox.
Launch is a time for a new IPs, so unless Microsoft hits a few good ones they are going to be in trouble as pretty much all their quality IPs save Halo, Forza, and Gears have been poached for the other systems. Sony still has boatloads of quality, exclusive IPs to pair with the new IPs that will be launched, so even if most of them fail, they have others to fall back on.
I don't intend to buy any next gen systems for a year or two, but knowing nothing about the two, I would probably pick the playstation as Sony's launch systems don't have a history of a high failure rate.