You can, in fact replace the piston and liner of an ABC engine (or a ringed engine for that matter). But in an ABC engine, I've always heard you replace them together. So it does cost more than just replacing a ring on a ringed engine. On the other hand, I suspect it's actually rather rare for an engine to actually get "worn out". Most, it seems, die from other causes long before normal wear.

Gus, I think you are right about the why of the taper. I was agreeing with the fact that the effect of this is that the surface friction of an ABC engine is lower than a ringed engine when running. I've seen that written more than once by guys who know a lot more about engines than I do. I'm under the impression that the taper plays a part in that, though I could be wrong on the overall effect of the taper.