BlondeBomber: Southwest Airlines doesn't publish a TUS-DTW fare, therefore it costs hundreds of $$$ more to fly from Tucson compared to PHX. I have to leave the house about a half hour earlier to catch a flight from PHX compared to taking a flight from Tucson to connect with the same PHX flight.
I havn't flown on Southwest Airlines for maybe 15 years, but I LOVE them anyway!