It's only useable by wizard and sorcerer, shouldn't bard be included as well?
Nope. Definitely deliberate.
Sorcerers and Wizards can be Abjurers. Can Bards?
Question was answered, excess input not required. I assumed it was an arcane wand, and bards manipulate arcane energy.
Hehe. I actually suggested this device as a way to allow Sorcs/wizards firepower without providing an easy consumable to Fighter/bards etc :D.
As a bard, you should be able to still use it, provided you have enough UMD. Unless there is some mechanical or role playing restriction on it.