Sounds like you know this stuff. The paragraph from Settel's book sounds believable though, because he's talking about the early 1920's. Didn't Edison have to go through hundreds of materials before he found a good filament for his light bulb? The others were too delicate. Maybe the same thing was going on with sound tubes in the early days, lots of experimentation, and maybe some of them did physically blow up when subjected to high frequencies.

Wikipedia says about "crooner":

Crooning is style that has its roots in the Bel Canto of Italian Opera, but with the emphasis on subtle vocal nuances and phrasing found in Jazz as opposed to elaborate ornamentation or sheer acoustic volume found in opera houses. Before the advent of the microphone, popular singers, like Al Jolson, had to project to the rear seats of a theater, which made for a very loud vocal style. The microphone made possible the more personal style. Crooning is not so much a style of music as it is a technique in which to sing.

The Wikipedia entry makes reference to the microphone as an influence on 'crooning.' I suppose the question of equipment failure could be answered definitively if anyone cared to do the research, but I just thought the statement contained in the original posting was interesting. Technology has always had a hand in the development of popular music. Look at how popular songs got longer and longer as recordings moved from 78 rpm to LPs.