They would have to do drastic redesign of terrain, pathing, and collision. When you don't have the knowledge of how these things work, "I doubt it" doesn't work as an argument.
And having to program a "manual" jump to specific terms wouldn't be work? Just how high and which of the who knows how many there are ledges would they have to program in , both in existing zones now and ones to come, to allow said manual jumping? Which cliffs could you jump off of, and which not. Which rocks could you jump over and which not.

And as a cs major in my 3rd year, with a personal interested in opengl api, I think i have some clue of exactly what would have to be changed to impliment a free jump.