both right, but the wall strength guy really is
At
http://search.us.kohler.com/?q=4509 i found, for K-4509 and K-4509-T, the Cayuga/Bolton Tank For Model Numbers K-3440 AND K-3475... I have seen these but never looked behind.
My wall-hung toilets are Euro style on Geberit carriers, not like these. I think there is rubbery ring. Maybe neoprene. For sure there is no wax. (For other kinds of wall-mounts, I have read about the difference in rings, here.)
My Geberit carriers are bolted to the floor. They
could support a toilet all alone, for a little while, but not for years. They need a wall or another carrier behind them (back-to-back) to bolt onto. Ask Geberit. Geberit insists on 6" wood studs on both sides, and bolts. Or better. No cheap and flimsy metal studs; they'd have to be reinforced.
I know because i pestered their tech support people for a long time when I needed to get to the bottom of this issue. I was arguing over the strength and adequacy of the construction that I saw happening, before I had to take over. (Chuck C is the boss of Tech Support at Geberit and Chicago Faucet, say hi for me. All his team is consistently good.) I would have had bowing drywall if I had let the former guy continue. And worse.
The problem with wall-hung toilets is that plumbers and builders have to communicate differently -- about different things. What needs doing and who is in charge and responsible and liable. Imagine a plumber telling a builder how strong the wall has to be. "Never heard of such nonsense."
But maybe none of this applies to other types of wall-mount carriers.
david