Pete Hines said on his Twitter there won't be climbing in the game, that combined with the podcast it paints the image pretty clearly that there will be massive mountains that you can't really move across at all, you'll have to follow paths and tracks up and through the mountain. We'll have to see when the game comes out, but that's what it all points to it seems.
Trudging slowly up a steep slope isn't the same as climbing. Some mountains may be so steep as to be untraversable, but I'm hoping most places will be. I never heard any indication of that from the podcasts.