I too have heard of enough people doing this that it concerns me. The logical fallacy of appealing to common practice is one of the most common pitfalls in all of knifemaking. The error of assuming that because a number of people do something that is must be correct should be obvious, but this is not the case on our craft. The other odd thing about our craft are the number of methods that are adopted for various reasons that can be at odds with the actual purpose of the operation, but when the exercise doesn't result in obvious disaster it becomes validated and the practice gain acceptance. If your priority gets skewed from knife edge properties to keeping things straight then any method that produces a straight piece of steel can be called a success. So many practices have gained acceptance because we simply changed our priority and redefined success.
We have three categories of steels we typically work with, "water hardening", "oil hardening" and "air hardening". Plate quenching was adopted long ago for air hardening steels and is slightly faster than air but is not a liquid medium. One can say that very thin sections can be done but very thin sections of O-1 can be left in the open air and get very hard, and with L6 in thickness of 1/2" to 5/8" I can get a consistent 61 HRC from just throwing it on the floor while hot, but I would never heat treat a blade this way. My famous killer lawn mower blades showed me this, I started out just welding L6 inserts in and then using air cooling since I could get a 61-62 with this down and dirty heat treat (it's just a lawn mower blade, after all). No matter how well I tempered these blades the inserts would break out in use. When I took the time to properly heat treat (oil quench) and temper the inserts I never had to replace them again and have been grinding up anything in my path with glee.
There are reasons the specific heat treatment of specific steels were developed, other methods may "look" good but it is what goes on inside that steel that matters. Yes there are more people playing with plate quenching steels that really should be quenched in oil, there are also a lot of people who swear by gooey lard quenches, but since I don't work with air hardening alloys I will not be quenching any of my blades in either.