I completely understand the need for "aircraft positioning", but, for example, if you have one A320 going MSP-DTW and one A320 going DTW-MSP, there is one less plane to reposition - which could be used to add frequency to an existing route, open another, or [gasp] retire a DC9.
There is usually a spare A333 in the system, though not sure that is the case during the summer (peak) season.
With 7 330 arrivals in DTW (4 in MSP, not counting HNL), there is wiggle room for aircraft swaps for weather, maintenance, or whatever reason.
CO does this all the time, shuttling the 76's and the occasional 777 between IAH and EWR. AA runs 777's DFW-ORD, ORD-DFW, ORD-MIA, etc, DL runs international 763's between JFK and ATL.
The occasional and inevitible delay/inconvenience would be made up for by utilizing 1 out of 11 $140mil aircraft that would otherwise sit parked for 4-8 hours more effectively.