Someone made a comment in the earlier Winnipeg jersey thread that said they'd actually have to buy the rights from the Phoenix Coyotes to use the old jersey. On top of that, while most hockey purists (such as myself) would prefer the old logo, creating a new one generates so much extra revenue for the owners. If they used the same logo, it gives people an excuse not to buy a new jersey or article of clothing.
I was under the impression that the rights to the old Jets franchise belong to the NHL. Naming, likeness, and otherwise.