It's not uncommon for people to take these approaches in fishkeeping. Some people swear by adding salt at every water change also to prevent Ich infestations.
Some strains of ich have been proven to survive far beyond 85 degrees, so it's not bulletproof, and 85+ is a little above the range that most people keep tropical fish in.
Anyway, I understand the concept of why one would do this, but proper QT procedures on new additions would serve the same purpose because Ich is not ever present in tank systems.
People often do things because it works for them in whatever way, even if the science behind it doesn't really jive.