There is a significant difference between the two. You can only gain the benefit from one of the combined staves at a time because they all give the same benefit to different spells. Combining melee weapons gives additional benefits to the same action.
If the request was to be able to wrap the magic attack, accuracy, and summoner staves up into one your point would be valid, but all we're really asking for is some inventory relief by not having to carry around 8 identical staves.