It's called the "shooterbox" not because of the sales of games, but because of what games are notable on the console. Skyrim, Batman, Indies.....those are available on both consoles, so they're no more definitive of one console over the other. I guess I was incorrect to list Red Dead, Skyrim, etc. in that regard. But compare both consoles. What games do you know the system for?
Because the drop menus are ordered by sales, this is just what I'm going by when I scroll down: for PS3, there's Gran Turismo, Uncharted, Metal Gear, LBP, God of War, Last of Us, Resistance, Motorstorm, Killzone, Heavy Rain, Infamous, Ratchet and Clank, Heavenly Sword, MAG, KH1.5, Virtua Fighter, Warhawk, Demon's Souls and Naruto, and that's just the over million sellers list.
On 360, there's Halo, Gears, Fable, Kinect stuff, Forza, Left 4 Dead, Crackdown, PGR, Alan Wake....and those were the only exclusive series I could find on the first page 200 games.
Look at the two lists. If we stretch the word "shooter", since you did so to say GTA is one, of 19 games or series that are only on PS3 and PS3 owner bought the most, 12 are non-shooters (I counted Uncharted, TLOU, Resistance, KZ, MAG, and Warhawk as shooters). Of the 9 games/series that are only on X360 and X360 owners bought the most, 4 of them are shooters (I counted Halo, Gears, L4D, and Crackdown as shooters). It hurts the 360 more because there's less to choose from, but near 50% of games or franchises you can only get on 360 (that you guys actually bought) are shooters. Hence why it's called the "shooterbox". Obviously there's games like N3 and Lost Odyssey, but those games aren't the perception people have when they think "Xbox", and the sales show it