The longer skirt does provide better oil control...
Now, I would say the real reason for the 'lack of mileage' is because most stangers that put money towards stroking the bottomend and using drivetrain parts that are beefed up typically have another means of transportation.
In other words, the strokers/G-Force equipped cars are 'weekend warriors'...
They aren't going to rack up the mileage, although I think several of them could hit 100k with no issue.
The 302 will last longer, all things being equal.