There's a lot of variables to tire life. As one poster so rightly answered road conditions change from area to area. Why this matters is that, for an extreme example, if you live in Hawaii your tires won't last as long due to volcanic rock used as asphalt which is very rough on tire wear, like riding on sandpaper vs regular Indiana rock which is not as rough on tires. Also depends on if you live in mountains where you are constantly turning vs midwest flat lands where roads are long and straight. Do you live in a very hot climate like the desert areas of California vs cooler areas of the northwest, midwest, east coast areas.
Different tires last longer then others. The longest lasting tire I ever use was the Specialized Armadillo All Condition Pro, these lasted about 4,500 miles riding mountain roads and hot roads of the deserts of California. Conti Gatorskins I recently had lasted only about 2,500 miles here in cooler flat lands of Indiana. My latest set of tires I just put on so the study is out. I'm trying the Kenda Konstricter tire to see if it's any better or the same as the Gatorskin in durability, they are lighter then the Gatorskins and feel faster-just me?. But so far the Kenda's feel better and have better handling then the Gates.