How many transponder equipped gliders, transponder on, have been hit by a
non-TCAS equipped general aviation aircraft? Is this really a problem? Can
it be addressed by training?

does that mean that having a transponder on board will eliminate this risk?
Does that then allow us to feel secure that it can't happen or won't? The
only way even with a transponder installed and operating to know what
traffic is around you is to be in contact with ATC....simply sending a
signal doesn't tell everyone around you that you are there.
tim