There wasn't much that was in any way clever in the characterisation etc in KR, but I agree that was a really nice touch.
Asimov's three laws are such a great plot device, I never realised he introduced a fourth law later on called (rather clumsily) the "zeroth" law:
0. A robot may not harm humanity, or, by inaction, allow humanity to come to harm.
1. A robot may not injure a human being or, through inaction, allow a human being to come to harm except where such injury would conflict with the Zeroth Law.
2. A robot must obey the orders given it by human beings except where such orders would conflict with the Zeroth or First Law.
3. A robot must protect its own existence as long as such protection does not conflict with the Zeroth, First or Second Laws.