I've gotten as little as 8000 out of a stock front tire and as much as 15000+.
For me it is very dependent on-
The roads I'm riding
The ambient temperature
How I ride
One weekend in the Ozarks I rode about 1000 miles, very aggressively in the twistys and in that 1000 miles I shaved over half the tread off of a brand new front tire.
I believe if I had a new stock front tire for a week and rode hard thru 2000 miles of twistys I could have a stock front tire completely bald in the center.
Conversely, I believe if I rode on nice roads, no twistys, in a conservative manner I could get 20,000 miles out of a stock front tire.
Since I like riding somewhat aggressively in the twistys, I am now running an American Elite rear tire, reversed, up front. It currently has about 15,000 miles on it and still has more tread depth than a stock new tire has. Plus it grips better than the stock front tire.
Kevin