Originally posted by Angrybeard:

I think they haven't done it yet for 2 reasons mainly:
1. It would take a lot of time and effort to develop and balance out.
2. Some weapons, like spears, would become obsolete (again balance issue).

Why would spears become obsolete? Being able to do the standard attack on slopes would be amazing (just as it would with the other melee weapons), and they still have a ranged attack option that works great in all kinds of situations, such as killing leeches without expending arrows or snagging that parry-crit on an enemy that got knocked back too far for a standard attack. I love spears, and I'd love them more if I could aim the melee attack, too! :D