I asked ... what would happen if I abandoned the rtw in the middle. I was told that the *entire* trip would be recalculated at full fare.

How could/would this actually play out? Let's take a simple case: you have a RTW ticket JFK-NRT-SIN-CDG-JFK. And you get to Paris and throw away the last ticket. Is there any chance that they'd come after you and try to charge you for the full point-to-point fares?