Why is it that the move order 1.d4 d5 2.c4 dxc4 3.Nf3 e6 4.e3 c5 5.Bxc4 a6 is played a lot to avoid the Furman variation, but why not also to get something else instead of all that Bb3 stuff? E.g. why does one not play 6.0-0 b5 7.Bsomewhere Bb7 or the like? Or maybe white should already play 6.Bb3 if he wants to be able to answer a2-a4 immediately if black plays b7-b5?! (there's also 6.d5 or 6.Qe2, of course...) This seems to be something that is generally ignored, why do all commentators seem to assume that 6...Nf6 (or on earlier mvoes) is a given?