tradition of the last TdF stage
As a sometimes watcher of the TdF I'm aware that traditionally the race is "decided" by the 20th stage, thought that one time it ended with a time trial may well be the only exception in the history of the event... it's the only one I've heard of anyways.
What struck me in the highlight coverage I've seen so far today is how definitive all the talk about the winner is. That's it. He won. End of story. This year isn't any different in that respect that what I've noticed in the past when I've followed coverage. I guess I'm a little curious as to the nature of this tradition. Is it because in most cases the margin is so wide by the time they're heading to Paris that it would kind of be asinine to make the leader chase down breakaways that contain riders close in time? If the time gap were closer (and the tour didn't end in a TT) would it be surprising if we saw someone try to make a play for it?
I'm also a little curious about the history of this tradition. Is it something that was there from the start? Or did it evolve over time in recognition that the leader's position is never really affected on the last stage, so why not just make it a kind of ceremonial kind of stage and all celebrate that we made it three weeks in one of the most brutal bike races in the world?