The guy who gets to Paris in the least amount of time wins the tour. Some cyclists do not do very well on mountains and are slower at cycling which is why they can not win the tour, some are specialists at mountain climbing but can not time trial. Depending on what you are best on you will race better on certain days.
To win the tour you have to be good all round, this year we were lucky there were not so many hard mountain top finishes and more time trialing then usual this allowed wiggins to have a great shot at winning it.
In teams you will have people signed up to do a specific job, much like in football we will sign a midfielder who can maybe score a few goals, but does that mean he should be a striker because he can score more then some of our strikers.
Froome surprised me with his time trials he did better there then i expected but also so did richie porte so sky have a couple of options going forward over the next few years.
Wiggins is a strong cyclist but in the high mountains he struggles to contain the better climbers. I think next year he will pace set for Froome and end up himself getting a top 10-15 finish.
The problem is that in a fairly easy tour such as this years one sky were unable or unwilling to chase down the attacks on the earlier stages and bring the pelton in as a bunch for cav to have his sprints. Now after what Froome said yesterday that sky want to compete for the yellow every year it means cav is in brick street. But reading this link i would assume he is off to be honest with you.
http://roadcyclinguk.com/news/racing-news/brailsford-cavendish-can-leave-team-sky.html?
Sky have a decent young cyclist in Ben Swift who can sprint a bit but i wonder what the make up of their team will be next year especially if the team time trial returns.