Two things I can see effecting this. One, "exact same shot" may not be exact unless you're talking about a dead-center hit, so you can get variance based on some randomization built in on the "miss". More than likely most fairways are not perfectly flat so you may get more or less roll depending on the contour where the ball makes contact with the fairway.
If I have a complaint about inconsistencies it's with the amount of left-right off-targetedness you get on even slight mishits. I can hit it fractionally before and after and have it be anywhere from fine to dead even in situations where there's no wind helping it into oblivion. Again, I attribute it to some built in randomness.