We definitely want to avoid as best as possible a single class being far and away better than all others at something (such as mobility) and thus used exclusively for specific tasks.
As long as there is choice and variety in the game there's going to be one solution that gains a general consensus as being the best at "X". The hope and the intent is to make the difference between the best and second best, third best, etc. as close to imperceptible as possible so that you can use what ever class/character you want, what ever build you want, and not feel that you're far and away below the abilities of something else. That's balance in choice.
We're taking a close look at what those specific mobility issues were in Diablo II and could be in Diablo III, and yes we're certainly trying to be a bit smarter about planning for it. You specifically mention the witch doctor. With the way he plays and feels a big warp or jump around skill just doesn't really seem right for him, but he may have a trick or two up his sleeve...
