Well, of all the replies in this thread, yours is the only one that actually addresses the original topic. Thank you for that. It is also good information to know.
I'd still like to know though, if sharpening, over time, will soften the metal to any appreciable degree, even if you don't overheat the blades?
Some of that depends on whether the blades were originally through hardened, or surface hardened. Obviously a surface hardened blade can have the harder outer "shell" worn, or ground through over time or with careless sharpening. It also depends on the composition of the steel alloy used.