The rings would definately wear down quickly at high RPM.
Plus, what is the compression ratio of these RC engines??? Anyone know?
I would imagine it would be higher than your average car or tuck at 8:1 - 11:1
Maybe the engines need a metal to metal contact with very little give to maintain high compression.

Also, with a 2 stroke, the crankcase isn't filled with oil, so if there is a small leak from the crankcase into the chamber on the downstroke, it doesn't matter.

Another thing is that a piston to sleeve contact will last longer than rings, im sure. But for a piston-sleeve to fit properly, it has to be very well engineered and VERY precise.

with vehicles with multiple cyllinders plus a cooling system, alternator, ETC. THe block has a lot more metal in it for everything to mount to and it will expand and contract a lot in high/low heat situations. The rings are kinda springy to account for this, whereas an RC engine definately has some expansion, I don't think it is to the same degree as a multiple cyllinder engine.

Just a few things that came to mind when I thought about it.
Maybe waaaay offf.