Don't aim for pixel perfection cross compatability, aim as best you can for it to work in the modern browsers with better standards support.
I've learned quite a bit about CSS, how it's used, how it renders and how powerful it can be by coding to the pixel for the goal of near perfection. Yes, on the practical level you make a great point and unless you have the time and patience I do not suggest for someone to take my approach. Still, I take on the philosophy: If you can get near perfection then do so.