Hm, in the books Robb is a background character, he never gets a POV and thus remains a bit sketchy.

In the tv-show he has far more personality, mainly because there is an actor playing him, giving him a 3D structure he simply does not posses in the book.

I think it fits the character to be popular in this phase, he's the young celebrated hero. Things take a turn, that's Martin. His death will be all the more shocking and interesting.