That attitude is fine up to a point, but in the end, 100mpw ends up being a fairly commonly run mileage by top runners, whether they are counting their miles or not. A certain amount of miles is going to have a particular physiological effect on a runner's body no matter what the runner's mental approach to running those miles is.
Also, if you were a coach and your HS or college runners asked you how much they should run over the summer, would you tell them to "train to race", and not worry about mileage totals, or do you think they would be more likely to come into XC season in good shape if you gave them a specific mileage program to follow?