Technically, he is correct, that according to the specs on Tire Rack, the revs per mile are not identical between the two sets of tires that came as OE for the Crossfire.

Here are the specs on the Michelin:

http://www.tirerack.com/tires/Spec.j...5YR9SPORTPS2XL

And here are the specs for the Continentals:

http://www.tirerack.com/tires/Spec.j...e%3D535WR9CW95

Each tire is 2 revolutions off from its counterpart.
The front tires are M - 829 and C - 827 while the rear tires swing the other direction M - 799 and C - 801.

These numbers mean that the tires turn XXX number of times to travel 1 mile down the road.

What causes these numbers to be different from each other, even though the sizes are the same? Simple things like the tread depth when new. Notice how both Continentals are 10/32 deep, while the front Michelin is 10/32 while the rear is 9/32.

Also, notice the difference in weight between the two sets of tires.
Running the Michelins on the Crossfire saves you ~8 lbs of unsprung, rotational weight.
I read somewhere recently that for every 2 lbs of tire/wheel weight that you drop off, its the equivalent of removing 150-200 lbs of sprung vehicle weight. I'm not 100% sure if I believe those numbers, but its something to think about.

Having to spin the heavier tires I'm sure has an effect on fuel mileage.
How drastic is that effect, I do not know.

BC.