I was just watching some of the Tour on TV and I had a thought of how much of the riders equipment is chosen by themselves or buy the team and managers.
When people ask question on these forums as to which bike, helmet or really any other of the many bits and pieces the answer is always along the lines of 'make sure it fits you and it's comfortable'. The bike and the helmet are probably of major interest here.
When watching the Tour all members of the one team seem to be wearing the same kit. I can't be totally sure of the bikes but they look the same throughout a single team or at least the colours are. The helmets within the one team are definitely the same. Sure they may use different spacers and what not under the helmet but it's still the same helmet. When I was trying mine on found that different colours of the same size and models with the same sized inserts felt different. So what do the professionals do?