Rotor heads, at least the ones I've installed and encountered, have a track record of lasting through the season, once a system is opened in the springtime, and heads aren't being destroyed by landscapers on a constant basis. Replace the soil I work in with sand, and maybe some of that changes.
As for systems lasting 20 years without a single head replacement, I would tend to call BS on that. Ten years, yeah, and I've installed them. But for double the life, you are getting into S-T-L territory.