The importance of the team setting the pace in the lead group is overblown. If Lance has three Posties leading him up the mountain, Basso has four Posties doing the same for him, doesn't he? The support from the team is much more important when there is somebody to chase down, and that is not the case that often the way this Tour unfolds. All stages end with a man to man fight this year, with all the domestiques gone. At that point it is much more useful to have dual team leaders than to have another domestique, as you can only make Lance chase if somebody important escapes. All the while before that point, when the domestiques are setting the pace, that high pace helps the strongest riders, whether they are wearing a USPS jersey or not.
As for the historical question, I think Tibbs' observation is correct but the end result is the opposite. Teams used to be much more structured with one leaders and the rest domestiques, so in a sense much like USPS. Slowly that has changed to include other riders in the team, riders who can go on break-aways, ride their own race, dual leadership, etc. A team like CSC wouldn't exist 40 years ago, it would be unthinkable that not every rider would work for the leader and do nothing else. Raleigh was one of the first teams to show up with a star-studded team, and after that teams like La Vie Claire.
Gerard Vroomen
3T.bike OPEN cycle