It is normal. But the point is that it is not required that an airport perform that check, in the same way there are requirements about x-ray and metal detectors, for example. Some airports just don't do the shoe thing.
Perhaps that's the loophole. Although my anecdotal observation at the generally major airports I fly in and out of in the US is that people are pretty much universally taking off shoes if they're not in the pre-check line.
