I just noticed the same on one of my best bikes. Rode it just now and it is riding perfectly (with or without hands) so it is hardly an issue, but still ... My thought is that I will take the fork off and lay the steerer on 3 hardwood 1 inch planks, fork on its side, and measure down from the dropout to the table under, rotate the fork 180 degrees and repeat. If these differ, I will coldset the blades a touch. If they are the same I will dress the dropout on the side the rim is on a touch. That fork is due to be repainted, so I will address this at that point.
Ben