No, it doesn't make much sense, noone ever struggled to distinguish these for more than 30 years - hopefully people can still READ!
No, most people don't read manuals. Most developers had to learn this the hard way.
Things have progressed since 1985 - GUIs are supposed to be self-explaining, albeit this presents an ongoing and sometimes impossible challenge, given the technical restrictions. Radio buttons are a well established paradigm for mutual-exclusive choices in AmigaOS since 1990, so it makes sense to extend it to menus as well. The rest has been said.
C'mon, you must have detected more serious flaws. Even we did.