It's impossible to win a GT with some of your team hunting stages; you need all hands on deck, because you are going to get attacked.It's impossible to do a serious attempt at GC, without a team to back you up.
It would make no sense, to just have one guy do GC, and the rest hunt stages.
It is eminently possible to go for top 10 with only one or two bottle carriers, and have other guys on the team do their own thing.
It should also be pointed out that the above only applies if the intent is to control the GT from start to finish. Let's not forget that the Giro last year was won by a team who were all stage hunting, for all intents and purposes, until the final week. And the Tour was won by a team who brought a 33 year old sprinter and his leadout man, and lost their best climbing domestique and a stage hunting climber during week 2.