You do not have to calibrate it, doing so will give you little benefit, and yes you can get a cheeper calibrator, but you will get no benefit on it using a ACD as any benefit would be very specific and would require much expense.
as per the second part, no most people don't buy them because they are expensive and the quality only makes a big difference for people who work in digital arts.
So what you are saying is that the ACD is perfectly calibrated out of the factory and will retain that throughout its life with no calibration? If that is the case you are deep in the reality distortion field.
The ACD is hardly perfect from the factory. Furthermore, displays change with age. That day one ACD will be different in 6 months. Most designers understand the benefit of a calibrator and they own one as well. Again, the ACD is not some magic display that will keep perfect calibration throughout its life.
As per your response on the second part, my point was that they are overpriced. And furthermore ACDs are hardly the epitome of quality as you are asserting. They look good, but there are much better for digital arts people.