<blockquote>In one case the video poster said that Whirlpool said the bottom support for the machine had rusted out and crumbled. I suppose this might explain why the off-balance cutoff switch wasn't activated, because the drum had droppped below the level of the switch?</blockquote>There's no physical off-balance switch on these machines. The control board software determines off balance by monitoring RPM, rotational inertia, and other factors (referred to as "bump detect").
There also is no bottom support. The tub hangs from the four corners of the upper cabinet frame via spring-cushioned rods. The upper frame would been what rusted (assuming it was a factor at all), not the bottom. I've heard in some cases there can also be a problem with the support rods contributing to excess tub oscillation. "Bump detect" depends on proper "operation" of the support rods.
There also is no bottom support. The tub hangs from the four corners of the upper cabinet frame via spring-cushioned rods. The upper frame would been what rusted (assuming it was a factor at all), not the bottom. I've heard in some cases there can also be a problem with the support rods contributing to excess tub oscillation. "Bump detect" depends on proper "operation" of the support rods.