DTW is a northwest hub. Because NWA owns so many gates, they make the market, for the most part. Spirit also competes on those routes, but few other airlines do. Notably, southwest is rarely competitive on DTW-MCO/TPA routes---even ding fares have been well over $100 each way.
I would bet that you'll find better fares out of the chicago airports.
If someone is conisdering DTW, they should also consider TOL and FNT. LAN is rarely a good deal to florida destinations. If ORD/MDW and DTW are both options, perhaps IND would be too---there are often good fares there, as several airlines are trying to fill the void left by ATA.