If the figures are correct, by itself R2's opening is impressive.
I think it's just the inevitable comparison with the initial sales of Gears 2 that gives the feeling of that it "lost". But 400k is not bad on anyone's book.
Maybe it should be a lesson for everyone (360, PS3, Wii owners alike) not to make the "Game X will pulverize Game Y" kind of predictions. Eventually, someone will lose and be taken down by it, rather than just enjoying the game, which we all should be doing.