I've always presumed that real aviators can fly their aircraft and listen
to the radio at the same time. If a "check gear" call rattles a pilot so
that he loses control of the glider, there's a problem afoot much more
serious than radio procedures.

I agree! If I was going to land gear up would be nice to have a radio call
from someone who noticed...snip...no reason to have a moratorium on alerting a pilot on
final...

In this case: "moratorium" = "catering to the lowest common denominator".
First priority: Fly the stinking sailplane! Second priority?: (If you must...)
Abuse it as gracefully as possible under the circumstances.

Head shakingly,
Bob W.