A properly installed toilet should never need the wax ring replaced unless it is removed for some reason. If the toilet rocks in the slightest, it is not installed properly, and it could fail minutes after installation.
Wax doesn't leak away (a rare exeption might be if hot water ran down the toilet long enough to melt it or there is a heater right behind the toilet, making the whole thing hot). It won't repair itself, though, and doesn't rebound, so if it gets squeezed too thin, then the toilet rocks the other way, it often won't stretch back, so the seal is broken.
A wax ring isn't like a rubber washer in a faucet. He doesn't have any science to back him up...make him show you something from a reputable source that says you need to change your wax ring on a periodic schedule...he can't.
A wax ring can fail if the toilet rocks, it is aggressively plunged (blow out), or too much heat, and it melts. Other than that, it should be good.