I think something else that factors into it is the more you piece and quilt the more your eye can see those distortions. When I first started quilting I didn't even recognize some of the imperfections that I now try to avoid. Not that it makes your quilt any less beautiful as some people find those little imperfections endearing. As long as you are not distorting your blocks to the point they look strange or they interfere with your measurements...and as you increase in skill you are bound to run into those types of issues.