Serious studies of transportation cost use dollars per mile, which is one reason why the bogus CNW Marketing study received ill deserved attention. When you look at the fleet studies:
http://avt.inl.gov/hev.shtml
You find the summary reports use terms like:
Operating Cost:
. . .
Maintenance Cost: $0.03/mile
Operating Cost: $0.08/mile
Total Ownership Cost: $0.29/mile
These are much more practical numbers but I agree, it tends to mask the individual vehicle performance. So they go on to report:
Operating Performance:
Total miles driven: 68,287
Cumulative MPG: 47.10*
It comes down to whether you want metrics that force 'long division' to calculate expected fuel burn or a simpler, multiply. The "<quantity>/mile" rating supports multiplication to plan a trip, which is much easier than long division required with "miles/<quantity".
Bob Wilson