Some people have argued
in a similar thread about this as well.
I was initially on the side thinking SoM should get a 0-turn cooldown, but an argument changed my mind:
Yep people got it down.
Wands are offensive weapons with a backup utility
Staffs are utility with a backup attack
Basically, wands are useful for the basic attacks, but have less combined attribute bonuses than staves do. Staves are meant more for spellcasting than attacking, and (at least according to some people) they have better stat bonuses than using two wands.
This is about how it worked in D:OS 1 EE. Maybe?
However, in D:OS 2, there is now Memory as a limit to spellcasting. Because of Memory and being unable to switch skills, Staves are distinctly less useful than wands right now. So if Staves are supposed to be for those casters who use lots of skills, then perhaps Staffs should get inherent bonuses to Memory even before magic item modifiers are considered.