Why do riders not take advantage of other riders misfortune Today on the Tour de France, Vincenzo Nibali attacked while Chris Froome was having mechanical difficulties. According to the commentators and Froome himself, that's something you just don't do. Apparently it's seen as unsportsmanlike. Where does this come from, and why would a rider not take every advantage possible in order to win the race? I understand why it would be in bad form to do something like that on a casual group ride, but it seems like any advantage you could get in a professional race would be fine. 

It's especially interesting because Nibali lost a lot of time in the first week due to mechanical problems and a crash. It seems from comments surrounding the occurrence today that it's only bad form to leave the race leader behind when he has a mechanical problem. Can somebody please explain this to me. In any other sport somebody who has an equipment malfunction is just supposed to deal with it, and nobody is going to slow down for them.
This compilation of articles on the subject goes into a lot of depth and sources some examples and opinions of some very notable cyclists themselves.
http://bfc.sfsu.edu/cgi-bin/unwritten.pl?Dont_attack_when_your_rival_suffers_bad_luck_-_Cycling

&quot;I don't know when it evolved,&quot; said Phil Liggett ... &quot;It's been a gradual thing, this so-called unwritten code. But now it is understood. You don't attack a fallen man.
&quot;The unwritten rules among elite bike riders hold that a rider should win through effort and talent, not through misfortune on the part of competitors.&quot;