I was going to mention in my other post what Barry hit on, the ability of the machine shop to adequately deepen the cuts for the rings. There's a critcal specified finish that's required on the inner surfaces of ring lands. It, along with other things, allows the rings to load, properly seal, expand and contract to meet a multitude of conditions.
I'm not trying to slam your shop but what they're telling you would give me great pause, to the point of verifying it myself or getting a reliable 2nd opinion.
Asssuming the pistons end up being fine and your shop was wrong, I would also question any other work that they accomplish. That's just me though...
My money's on them having the wrong rings.
Let us know what it ends up being...
Dave