Thought it's not extremely likely to cause a huge amount of pull (some pull is more like it), this condition can be caused by a separating belt in one of the tires. Our '02 Legacy had this happen when we bought it new. Brought it in to the dealer and, after several tire swaps (front-back, side-side, cross rotate) the issue went away. We didn't do anything more about it but a few (maybe several?) weeks later a tire failed on the highway. Bridgestone dealer didn't want to do anything to warranty the tire at first, but with the service records from the dealer it was enough to convince him (the Bridgestone dealer) that it was a separation (tire flaw and failure) that did it. New tire, no more pull no matter how the tires were rotated.