Actually, At&t has stated that the majority of of their unlimited customers don't get throttled which would imply they are not exceeding the 3GB 3G/5GB LTE limits. People that exceed those limits on unlimited plans are a minority of a minority. In fact, I bet 99% of unlimited users never exceed 20GB.
There is no issue with throttling unlimited users. There has to be a limit. Or else, there will be a few abusers. The issue I have with the throttling is that it is based on arbitrary, fixed limits. It has nothing to do with maintaining the network. It has nothing to do with ensuring a quality experience for all. The only explanation that seems to match the implementation is that At&t is trying to push us off the unlimited plan. They are discriminating against that plan type in order to drive customers away from it.