No forced draw with insufficient material to mate?

Just lost a 5 minute live game with 2 pawns and knight versus bishop.  On FICS (a different chess server), this would be marked as a draw because white has insufficient material to mate.  Here, white wins on time.  Why doesn't chess.com test for insufficient mating material?  It encourages people to play the clock; I don't think that's a good thing.  I'm sure a million others have posted on this theme previously, but I thought I'd add my voice to the chorus.

You can helpmate so there is sufficient material.

http://www.fide.com/component/handbook/?id=124&view=article

6.9 Except where one of the Articles: 5.1.a, 5.1.b, 5.2.a, 5.2.b, 5.2.c applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by the player. However, the game is drawn, if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.

Great explanation

My apologies.  I should have specified forced mate.  I'm not arguing that losing in such a position is objectively wrong.  I'm simply pointing out that other servers make a different provision for scenarios in which mate can't be forced.  I prefer this approach because it provides players who spend time thinking about their moves an escape route should they be unable to win the game under time control.

@dalephilly: Maybe increment is worth a look.  I have not played with it previously, but it certainly would prevent games from ending in this fashion.