Its not the tube that's the issue though, its the fork crown. On most suspension forks these are cast not machined, (though yes my surly rigid fork is very crisp at the crown…) and in the case of all my other forks seem to be powder coated or painted. Add to this the methods most of us use to remove old crown races and you could have a recipe for a crown that is slightly off 'exactly perperendicular' to the steerer tube. When you're dealing with the tiny ball bearings in cartridge headset I think its conceivable that it could make a difference.
Mind you, I have had a steerer bind a little even though I thought the crown race was on properly, and after hefty re- malleting of the crown race (I use the inside tube of a car axle stand) it was gone.
Anyone know if a front end impact could bend the steerer/crown join and induce the same problem?