rule question for timed games

Because you ran out of time.

I have a serious question though - 

why is it a loss on time if you have a dead drawn position (say K+P vs K that's drawn easily, and black times out) yet its a draw if its K+N vs K+B, in which case checkmate is still possible!

Yeah, you need to play very badly to lose in the latter case, but in the former case you have to play badly as well. But shouldn't the point be that the clock ran out, and if mate is possible, then you lose?

So why do I lose if I'm winning and time runs out ???

If the game ends on your turn you lose no matter what ?

Yes, if your clock runs out, you lose. The only exception being if your opponent does not have enough material to checkmate you.

@cherub: The site uses USCF rules in regards to timing out. Helpmates are considered a draw.