Yah, those kind of "flare ups" where the flames are rising from the flavorizer bars to the bottom of the meat is fine. Maybe even a good thing. After all, that is the theory behind the flavorizer bars, is to burn off the juices providing a smoke flavoring for the meat. It when the "flare up" begins burning under the flavorizer bars, down in the drip tray that things get dicey. As long as you keep that relatively clean down there, it won't happen.
As Jon alludes, it is probably a lot of financially well off folks buying those huge heaps of stainless steel to cook a few burgers at a time. My guess is they are predominately white collar execs and such and are much less apt to keep up with maintenance, much less have a clue on how to maintain those things. I can just imagine what a big flare up in one of those things would look like. Maybe just push it down the drive way with a broom handle and let it burn. hahahhahaha