First of all, i don't think we are talking about the same kind of leg.
On seasons 1 & 2, it were double-lenght legs, last team to arrive on a double lenght leg is never eliminated, or penalised or something, it was one leg divided in two parts. And on season 3 it was a no-break leg, two different legs without a break between them, and since they are two separate legs, they can either don't penalize the teams, give them a speed bump or even eliminate them.