If you didn't see the race then why comment?
Because it is unclear from the clip if that was from during the race or after. If it was during, it looks like cadel was giving away a win. If it is after, it looks like a congratulatory handshake. I was curious what I was looking at.
In what professional race, or even amauteur racem would someone ever give the race away and go to shake hands before the finish line?
I can't begin to count the number of times I have seen breakaway companions approach the finish line and shake hands or pat each other on the back knowing that only one of them is going to win. Usually one or the other knows he or she can't contest the sprint and accepts second place. Sometimes the rider just sits up, sometimes they attempt something resembling a sprint, but both riders know who is going to win.
Considering the pre-race interviews and Cadel's comments that the national jersey wasn't all that important in the grand scheme of things, it didn't seem implausible that he would let the younger rider take the accolades on the day... especially given the clip and no other information. I only knew Gerrans won and Evans was second.
But if you think cyclists don't often and regularly concede defeat and accept a second-place finish you are delusional. It happens all the time. Not always in such a sportsmanlike display as a handshake, often simply dropping the head and sitting up, but often with a congratulatory word, handshake, pat on the back, etc.
Here is one example.http://inrng.com/2011/02/the-handshake/
Here is a more subtle example.
I won't comment on the suggestion that riders might actually buy their victories...