a polished surface disrupts the flow of air. again, why do you think the wings of an airplane are not smooth? If they were, that plane wouldn't fly well, thats for sure!

Your next question is going to get an answer that'll definitely hurt...

That polishing isn't going to last very long after the engine gets broken in and cycled. thus, making the whole process of doing so a complete waste of time.

in depth:

Furthermore, polish is not only unnecessary, it's actually harmful, in two ways. The first concerns the airflow itself. The experience of countless engine builders, plus research by Superflow, Boeing, and various members of the Society of Automotive Engineers, indicate that a smooth surface is not necessarily the slipperiest where air is concerned. Ever notice that an airplane's wings are not shiny smooth, but rough? The rough surface reduces air drag, and the wing glides through the air easier.

The second way polish is bad concerns combustion. Intake ports don't just flow air, remember. They flow an air/fuel mixture. The same lazy air boundaries that constrict a polished port's airflow also make fuel "drop out" of suspension in that air. The mixture then enters the cylinder less thoroughly mixed, and poor combustion and reduced power result. The slight roughness creates tiny eddy currents which keep fuel droplets suspended in the port air stream. Good combustion is thus ensured.