Yes and the way mogas and avgas is measured is different, kind of like saying jet-A and diesel are the same. Yes you can run a diesel on both, but they won't be the same.
At the end of the day, you can run a 540 on 98RON, but under very particular operating conditions, provided the state of tune is very accurate ( how many are) and if you can recognise detonation and prevent it.
Well aware of most of the old wives tails, maybe in the days of higher octane avgas lead served to reduce valve wear, but unsure if modern lyc's and conti's still suffer. So I stand corrected.
Also doesn't mean they are an acceptable engine for the future of GA, maybe keeping the current crop of aircraft operating, (which is I think what my original comment was about) STC's to allow them to run mogas would be cheaper (than developing an entire new fuel) via electronic engine control systems like FADEC but simpler, more in line with an '80's car engine.