" it's also a possibility if any DIY'er built their own car." 
Nothing to get excited about, Ed. Happens probably more than one might expect, on modern and antique cars alike.
On modern cars there are eccentrics available (no, not guys like me.... The mechanical kind) on the suspension to make dialing in caster and camber very easy.
On the older cars (like ours, if they're pan based) it's more of a brute-force mechanical intervention by using shims (front) or wedges (at the rear) to get things where the "Sainted German Engineers" want them. Either way, it was no big deal back then, and no big deal today.
As far as the DIY part, sure..... It's almost too easy to cut your pan in two and then weld it back together using 2" X 4" boards as alignment fixtures and have it a few degrees off. If you ask anyone who does car alignments for a living they'll tell you it's less common to have a warped suspension on modern cars, but still no big deal on the older ones, either - They just see what it is and correct it.
If it can't be corrected, then the next stop is a chassis re-alignment rack where the car has chains attached at various points and then hydraulically pulled back into a straight(er) alignment. This is far more common for big trucks (there is probably a rack within 10 miles of most large truck stops) due to the torque stresses of BIG engines under BIG loads.
Anyway, I have one caster shim on the Driver's side and two shims (one custom thickness) on the Passenger side. No big deal. Tracks straight and stops straight and does not "bump steer". Works for me. Of course, it helps to have an alignment tech who knows what they're doing, as most Voc School grads seem to be these days. My guy, "Tony-with-the-Mohawk", did an awesome job.