Believe me, wear might not be a concern for racers with big budgets, but for small part time racers, engine wear is a huge factor in their decision to choose an oil. If a particular oil can keep their engine rebuild frequency down, they can save mega $$$ over the course of a year.
Remember, not all racers can afford to rebuild their engines after every single race, only those with sponsors with deep pockets. And there are a lot of different forms of racing out there, not just NASCAR and CART. There are a lot of guys out there every week running their local stock car tracks, and they certainly don't rebuild their engines every race.