Halo 3 sold more than the Resistance 1+2, Killzone 2, Uncharted 1+2 and God of War 3 combined. Halo4 was somewhat round 12 Million Copies and the Gears of War Trilogy combined sold probably more than those previous Sony Exclusives and their Sequels.
Its true, Microsoft produces less games, but sells more of them. Worldwide.
Look up the GT worldwide sales numbers.