Lots of factors can cause all sorts of answers regarding car tyre life.
In general the better the quality of the tyre the longer it lasts, Michelin are the best for life. They will do 25,000 miles no problem.
Tyres from the likes of Goodyear last a good time too, expect in the region of 20,000.
Mid range tyres can go anywhere from 10 to 20 thousand miles.
Cheap uber crap budget tyres sometimes last a while because the rubber is so hard and lacking grip they hardly wear.
Its important to have the tracking checked reguarly too, that being out can cause excessive tyre wear.