well, when Jethro Tull first started everyone thought they were terriable and wouldn't rebook them or book them at all, so they kept changing their name around. Their name just happened to be Jethro Tull at the time when they were asked for the first time to return to a venue. Apparently they hate the name.
The The name came about from the merabers wanting a name that was even more ironically detached than The Band (Rolling Stones has The Band ranked as #50 in top artists of all time just in case anyone didn't know of The Band).
They apparently wanted Robbie Robertson to feel like a complete and total *******.