This may in fact be an illusion, similar to eyeballing a chainline etc.

I feel like my commuter leans to the right a bit; one can sit there and look for problems all day long, but in reality it's probably the way your body is positioned, the particular point of rotation your crank is at, and the grade of the surface you're riding on.

Remember that a 20lb steel frame flexes a lot; if all of your weight is positioned on one side of the bike, of course it's going to lean in that direction.