[4. Nf3 is] A bad move.
Total nonsense.
Actually it is a bit more flexible than 4.d4, as white may delay this pawn move for a while, e.g. in favour of Bc4.
But usually both 4.d4 and 4.Nf3 end up to the same positions.
d4 cxd4 Bc4!
http://www.chessgames.com/perl/chessgame?gid=1639984
White played with the technique on an earthworm.