2007 Subaru Forester Wheel Alignment

Tires and Wheels problem
2007 Subaru Forester All Wheel Drive Automatic

I just had my 30K service on my Forester. I had to replace the tires and have a wheel alignment. This is the second wheel alignment this year, one in February and one yesterday. The dealership, of course, tells me that is just a matter of tire pressure. I hear from other Forester owners that they run with an added 2-4 psi pressure. I am trying to determine if I have a serious problem the dealership wants to ignore until my warranty expires, whether I'll just have to have the alignment checked every six months or so, or if there is something else I can do. It seems to me that I should not have to replace tires when the car is less that two years old, and I drive on well-paved roads.

Any advice would be appreciated.