I would imagine that they run a Factory Peroformance Part. Like a GYTR. When your a factory rider or any sponcered rider you dont have a choice what you run.
IF K&N's are pices of crap then why do Baja 1000 Trophy Trucks run them? I dont think there are any other race vehicles that run in a dustier condition than them.
If your super paranoid about dirt getting in to your engine, but want the best flowing filter then run an Air Force Pre Cleaner around a K&N. The add a 2% air flow restriction but stop 90% of fine dirt before it hits the K&N.
One more thing. Any air filter will let dirt though foam or fabric. Why do you think 4 stroke's have an oil filter?
http://www.knfilters.com/airforcewraps.htm