Setup is important to correct a uke that left the factory in a state that is not good/not good enough.
That being said, factories send ukes, that they think are "good" or good enough.
Generally, the higher end the uke, the less chance that a setup is even necessary.
I think alot of times, the "setup" is more of a final quality control check/fix the store does before they send it to you. The store has incentive to check it to ensure it doesn't get sent back, because then they have to eat the shipping, and they have an unhappy customer. If you buy a uke somewhere else, and take it to get "setup" then it's more of a corrective thing, but really stores shouldn't be selling ukes that "need" a setup because it means something is wrong with it brand new.
Alot of ukes.. nothing actually needs to be done. They check it and if it checks out, they ship it to you. If it's a simple correction they'll do some work, or if it's not easily correctable, they send it back to the the manufacturer.