I would not assume that. After reading a bunch about tires here and also on the Crosstrek forum, I have noticed a trend with regard to tire life reported:The OEM Geolandars on my Crosstrek were at 7/32's out of 10, on my 40kmile Crosstrek when I sold it to get the Forester. Sounds like your alignment was off, or you didn't regularly rotate per spec. They are extremely long lasting tires...
Folks who drive in flatter areas, with less curvy roads, less severe rain and snow (like the above person from Atlanta) report high tire life. Those of us who drive in mountain areas, carving canyons regularly, live with snow or rain, etc report less tire life.
IE. I'm in the Pacific NW and can tell you for sure the roads around town (and of course in the mountains) are much rougher than what my family in ATL drives on. We get so much rain here, our roads are made rougher for traction. Also other small issues like the road crown is sloped more, most roads are curvy/twisty, even in the metro area, etc all wear down tires quicker.
Then of course there is driving style.
But anyway, getting 30K out of the Geolanders isn't bad, considering the driver is in Wyoming.