Model Fs have NKRO by default because they're capacitive boards, from what I understand. The trick with that USB adapter is getting the full NKRO over USB to begin with, since it's usually limited to 6KRO + modifier keys (Ctrl, Alt, Shift).
The Model M was cost-reduced in that they changed the capacitive sensing PCB for a membrane switch layer, but kept the buckling-spring mechanism for the keys. Because they didn't fit diodes on said membrane sheet (don't know if it would be feasible to do), they had to limit the rollover to prevent "ghost" keys from triggering when not pressed. It wasn't much of an issue for business applications, of course.