Realization from exchange with
C3PO, unlike R2D2, was premium mediocre. Mediocre robot with superfluous "premium" features (anthropomorphism).
Most anthropomorphic robots are PM unless there's a reason for it. The reasons to make robots human-like are weak.
Conversation
At the risk of looking like one of those nerds... Threepio was designed for social interaction and having more visually in common with humanoids theoretically makes him easier to relate to.
1
the weakness of that argument for going anthropomorphic is why he is PM. Is your google translate app in the shape of a "protocol droid"? :D
The app is virtual and lives in a piece of shared hardware designed for a different original purpose (and designed to be carried and held rather than to self locomote), rather than being a piece of hardware.
Considering people's mental models and expectations in an effort to ease a process is not unheard of when designing hardware interfaces. Switching gears a lot I assume you consider art to be PM?

