(when attempting to win on time an utterly drawn position)
Either you have money / fame (?) involved in the game, in which case, in my optinion, "the end justifies the means" and you can try to win at your leisure, either there is no stake and chess ethics plus comon sense should tell you that's tedious and stupid to go on. That's not the kind of win you are going to brag about anyway.
Let me ask you a question: If it takes you six minutes to reach a drawn position against your opponent, and it takes him forty minutes to reach this same position, who played better? He ended up with a position no worse than yours, but perhaps that was only because he took the luxury of thinking longer than you did. With this in mind, is that claim on time (or attempt to time out the opponent, punishing him for taking too much time) looking quite as trivial?
I don't know if the above is "common sense," by your definition, but it's some sort of sense, in any event.
Don't you think that's a little lame? I do, namely because in the situation you were mentioning, black would be better off without a rook, instead having just king vs king and bishop.
I'm pretty sure the rule is slightly different, not only because of logic but because I have seen this before in blitz:
If your opponent can't possibly mate you with the material he has, then he can't win on time. Since the player with king and bishop doesn't have sufficient mating material, he can't win on time; only his opponent can (because king and rook is sufficient mating material)
Doesn't it seem more plausible that this would be the rule, rather than the one you brought up?