Doesn't using Staves technically allow you to utilize the 2handed combat ability, to increase the critical damage multiplier? Granted, probably not exactly worth it in most cases.
Wands also allow you to use 2 runes, instead of 1.
As for bows vs xbows; It's just as people said before. The movement penalty is next to nonexistant. I usually use a single Tactical Retreat at the start of combat (or just position myself before combat even starts) and don't move from there in 90% of the cases. There simply isn't any incentive to actually try to kite enemies using a bow, when you can just chain cc enemies in most cases. Or outright kill them before they get to do stuff, for that matter. The only times I actually move and would consider using a bow are during early to mid act 1 and very rarely during bossfights, when I have to move out of range of a silence for example. Unless I just kill/chain cc them before, of course.
The added accuracy bonus on xbows is simply the added bonus, which allows me to use a +crit rune in my amulet, instead of +accuracy.