I would never have believed how much effect tyres can have on an apparent alignment problem until I bought an '03 Focus last year. The front tyres were "Teflon S**te" (tm), and although it ran straight, the steering wheel was as much as 20 degrees off.
I took it to get a full tyre set, and asked them to do the tracking, explaining how far the steering wheel was out. They told me they had checked, and the tracking was spot on; they said the problem was the crap tyres.
I drove away totally disbelieving them, yet within 100 yards, I realised they were right! The steering wheel was dead centre.
I've never experienced that effect in 46 years of motoring; you really can learn something every day.
Chris