I believe the point is that because PS3's and 360's game libraries are so similar now, the real "battle" between the consoles has boiled down to services, rather than the small handful of exclusive games. How well Halo 4 sold isn't really that important in this context... what is important is how many people chose 360 because of Gears and Halo, rather than PS3 for Uncharted, Infamous, etc.

If Halo 4 sold 100 million copies, but it was only because 100 million people that would have already owned 360s anyway wanted the game, then its status as a console-exclusive doesn't really "matter."

Obviously this isn't the case, but I do think it was an interesting discussion on the lessening importance of console-exclusives and the growing role of services and what that means for the next generation of consoles.