That's exactly the point. If it did not cost Yamaha any extra money to adopt Audyssey, Yamaha could keep ALL of its current fans, PLUS also TAKE AWAY some Denon/Marantz fans who must have Audyssey, but may want to try Yamaha.
Honestly, I couldn't care less if my pre-pro or AVR is Denon, Marantz, Yamaha, Pioneer, etc. But if they all had the same Audyssey XT32 DEQ, I may buy Yamaha if the price is better.
IOW, many of us follow Audyssey XT32 DEQ.
If Denon were to drop Audyssey and Yamaha were to pick up Audyssey, we would get Yamaha.