When losing in blitz, is it rude to play to win on time? In blitz, I frequently find myself in a position where I'm hopelessly losing on the board but have a good chance of winning on time (and the other way around). Is it generally considered good sportmanship to resign or offer a draw in such positions, or is it fair play to frustrate your opponent until his clock runs out?

Update: I realize this question is very similar to a previous question, although I believe this scenario to be slightly different, which may elicit different answers.
No it's not. Your opponent spent more time to reach a winning position and you spent less time to get time advantage. It's quite fair to use your time advantage over your opponents position advantage.

Time control is a part of chess.