I was wondering how much efforts will be invested to preserve GC positions considering only a few seconds separate many of the contenders. Wouldn't they naturally prefer letting domestics take the glory of shinning early?
GC contenders need to be very protective of any time advantages they have over others. I looked at Contador's results stage by stage when he won the Giro, and he finished way behind the stage winner on a number of days. If I remember right, he didn't win a stage. On most days, the GC guys will mark each other and just finish in the peloton. On stages with mountain finishes, they might finish together in a small group. Time trials are the best chances to differentiate. But if I have a 3 second advantage on you during regular stages, all I have to do is finish in your group every day and I win (assuming there were no bonus seconds available to either of us).
Domestiques don't tend to have a shot at glory. Sprinters do. Climbers do. In some instances, riders in breakaways can, but if they're ten minutes ahead of their leader they really aren't domestiques. Those guys keep the leader safe, get them food and beverages, handle rain gear, and do lots of other duties, even giving up a wheel or their bike if need be. You can't do any of that if you're up the road. And the peloton is very elective about who they allow into a break. It gets even more complex when the composition of the break dictates which teams do the work of chasing.