Bobby...
When you say:" Some have told me that some companies only post the accuracy numbers or repeatability numbers of the best axis."
What you need to remember is that even if they did publish numbers, they NEVER give numbers under load. That number is what separates the men from the boys, or "machines from the toys". Some use the linear equivalent of their preset step resolution, often for the highest resolution axis. Most every machine out there is capable of sub .001 step resolution. Because they can be set to that. It is the quality of the drives, motors and mechanical components that will determine if the bit will actually get to that position on a repeatable basis. The quality (read as cost) of those components is what determines the price category of the machine.
What this means in layman's terms: If you put a 1/4" bit in the machine and cut a 4" circle or square will it actually measure that when I am done? Answer is: usually pretty close, give or take .005" to .010" and the more experience the operator has, the closer he will get. The higher priced machines with higher priced components will simply do the job easier and in most cases faster. Lets say that a $10K machine can hold .005 tolerance, which should be more than adequate tolerance for wood, at much higher feedrates and depth of cut than a $2.5K machine can. Its that simple.