Good point rkporsley! Been there, done that.
I'd like to point out another often overlook thing, that I've seen in my shop many times. A near microscopic layer of corrosion between a battery terminal and battery post. You usually can not see it, unless you remove the terminals. They can look pristene, before removal. Removal is required to inspect any terminals.
And, this happened to me recently, after one of my free oil changes and multi-point inspections, Subaru gives us with new cars, which includes the battery terminals and water. I was surely pissed, yet not surprised, at the service department.
But be sure, this could have happened at any dealer, not just Subaru. (first and LAST time anybody besides me, works on my car... I hope)
Long/short, my 9 month old Outback would not start, 3 days after Subaru dealer inspection. Five mins with a wire brush and all fixed.
About the oem battery, all manufacturers put in small 3 yr batteries. It's really about weight and mpg. But they are not crappy, they are just small. With proper use and maintenance and no major overuse/high drain problems, they preform fine. Don't forget the water (distilled only). Check at least twice a year. Mine needed 24z when I gave up on dealer and resumed my own maintenance.
I always get 7-8 yrs from batteries, after oem wears out and always replacing with largest possible group size and longest warranty option. They always last 1-2, even 3 yrs past usual 5-7yr warranty.
I also agree completely with ammcinnis, this is NOT a Subaru "thing".
50+ yrs as foreign car mechanic and Subaru IS, hands down, the car for me. Even after putting about 600k miles on Toyotas, the worlds second best car. I love both companies. I won't digress (much), about how these companies have had a very tight relationship over the years and until recently, owned significant portions of each other...
I hope some of this ramble helps...