A lot of stars and champions move on to a support role in their later years, in all kinds of sports to include cycling. Very common, and many see it as a responisibility to stick around and use experience to give big brother advice to the new, younger stars and champions.
As far as the Tour de France...commercially it is the biggest race, but many pro tour riders do not see it as the greatest race. The Giro, Paris Roubaix, and others are often seen by Europeans as the most romantic, dramatic or exciting races, and they are still dominated by Europeans. Personally Paris Roubaix is my favorite race to watch, but it never is on TV where I live in the US.