I concur with Smitty.
Rear wears faster and that is normal and expected.
My riding style happens to fit with Smitty's numbers as well but that is really rider dependent.
Hard take-offs, hard braking, twistys vs. highway, one-up vs. two-up, all impact the number and miles you get. Additionally some tire manuacturers make tires from different compounds which are harder or softer. Softer will obviously wear faster, but provide better grip. I have only used Dunlops put on by my local dealer.
I think I could get a little more milage out of my rear before I change it but when it rains, I want a little more tread than the minimum for safety. (I got a little "fishy" in some heavy rain and it made me pucker. Now I change my tires on tread depth rather than miles. I don't wait to see the "warning bands")