Have you taken a look at the tire grading information on the sidewall of those original equipment tires? The rating for wear might range anywhere from...lets say something in the "200 range"...all the way up to the "700 range", and the higher the number the more wear you are likely to get from the tires.
I can tell you from experience that the OEM tires that come on most cars are not rated very well for wear. For instance, the ones on my friend's RAV-4 were rated at...240, IIRC. They wore out in about 25k miles, but he does mostly highway driving and he keeps them inflated to about 3 lbs over the recommended pressure, both of which helped him to get a few more miles out of those tires.
When he recently got new tires, I guided him toward the Goodyear Fortera Triple-Tread, an expensive, very highly-rated tire with a wear rating of...something over 500 IIRC. I expect him to get at least 45-50k out of these tires. In other words, you get what you pay for, and most car manufacturers really "cheap out" on the OEM tires.
Please check the wear rating on those tires and report back to us with this number, as this could be a very good clue as to your situation. Oh, and the internet abbreviation, OP, refers to the "original poster"--YOU!