I have a feeling there's going to be a lot of people choosing archer characters and jumping on top of roofs and stuff, where melee chars can't get to them 
Archers posted on roofs is not really a problem.
I fear something else : In that first video early on in the thread, with the two swadian men-at-arms attacking a village with some foot soldiers defending, you have a character that goes up a ladder, reaches the top, then jumps off and all the time, he is moving
backwards facing his opponent with his shield held up and weapon in hand.
So my fear is that hand to combat on foot will degenerate in the kind of silly to-and-fro, dancing-around-the-target and frantic bunny-hopping action that you see so often in all the online FPS games out there. I hope the devs have thought about that.
The impact of jumping, climbing, running and falling of heights on the multiplayer part of Warband should be considered very carefully.