Mate-gate: Rules can change?

I'm a little shocked that Richie Porte was penalized for two-minutes for a sportsmanship/mateship assistance from fellow Aussie bud, Simon Clarke. Today's stage was frantic and in the heat of the moment Clarke gave Porte his front wheel to replace his flat front tyre. Two minute penalty puts Porte in 12th overall, 3min 9sec behind Contador.  Here's the rule...

Rules can be changed or in this case ruled out by a act of friendship/mateship. Isn't cycling and other sports also embody fairness and friendship? In this instance... with rule attached.