The 4...Nc5 line clearly differs from the mainline you've given, since the knight on c5 will not be traded on g5 with black's pawn structure getting somewhat compromised. However it seems like the immediate knight retreat has some drawbacks since white can just play d4 immediately and kick the knight around a bit; note that after 4...Nc5 5.d4! Nd7 white can suddenly play the pawn sacrifice 6.e6! with a nice position.
Looking in my opening database I see that the most common move for black after 4...Nc5 5.d4! is 5...Ne6. In this position it seems like white has a pleasant choice of several good alternatives. For instance, 6.Be3 develops a piece and makes it a bit more difficult for black to play ...c5, while 6.f4!? seeks to gain even more space and to further kick the black knight around.
Basically, after 4...Nc5?! 5.d4! it seems like white gets a phenomenal position with a space advantage typical of the french defense, but without any drawbacks since black's knight loses so much time on its journey around the board.