I'll answer your question with a question.
If 360 had launched a year after PS3, cost $200 more, been a bitch to program for, and lost almost all of its third party exclusives to PS3, do you think it would be within 2 million of PS3?
Of course not. The Xbox brand is NOT anywhere near the same strength as Playstation. PS3 did EVERYTHING IT COULD to lose this gen and is still going to end up ahead of Xbox. If they launch at the same price and make an easy to program for machine, PS4 will most likely severely outsell 720. People say Xbox has the US and UK locked down but PS2 dominated those regions (like every other region) and that didn't stop them from switching this gen.
When people see all the exclusives on PS3 they usually gawk and want to trade in their 360. I've already personally converted 3 people just by having them look at the lesser known titles (basically anything other than Uncharted and GT). It's advertising that is still killing Sony and they need a revamp of their marketing department. Get that competitive and they will crush Xbox next gen because everyone will know the superior games on PS3.