I feel it isn't predominantly about racism or perceived racism among Latics fans, but the same reasons as why there are only 3-4000 home fans of any ethnicity in a town of 250,000. Most kids are brought up on a diet of saturation TV footballl coverage so they (armchair-)support big, glamorous clubs that play attractive, exciting football like United, City and Liverpool. Asian kids are no different from their white counterparts, hence you see them wearing united tops. The fact there were more Asian kids and parents when we played Liverpool or Everton bear this out. They came not so much to support Latics as to see Premier League stars in action right on their doosteps. If we get a new stand, and if we get promoted and start playing more attractive oppositions, I'm sure more will come through turnstiles, including Asians.
Also historically, in the Indian subcontinent, the No 1 sport has been cricket and in UK there are still more Asians of all ages playing cricket in local leagues than football or rugby. Evidence the fanatical support for their touring team when they play England in tests, one-days and 20/20s.
Other towns and cities with large Asian populations like Luton, Bradford, Blackburn, Leicester or Birmingham don't have significant Asian fanbase, though some perhaps do better than others.