Liggett is one of the most experienced and respected commentators working. He's done the last how many tours? Thirty? Something like that. He's also a race organiser and commissaire and is head of the biggest grass-roots cycling organisation in the UK.
Sherwen had a long career as a trusted domestique in France. He specialised in northern cobbled one-day and short stage races (his team was based in Roubaix for years)but rode (somebody correct me) nine tours and finished seven.
Bob had a short but lively european career, beginning as Sherwen's was ending. His roles on TV are as the insider with the irreverent angle and as the American connection. The Americans who raced before the Seven-Eleven team was formed had to conform to the old conventions of training and behaviour- to fit in with French, Italian, Belgian and Spanish ways of seeing and doing things. Bob represents the views of those who dissented from that and tried to forge their own, American way forward. Even in the comparatively liberal 7-11 camp, I think Bob pretty quickly decided that the grind of a long European season was not for him, hence the switch to mountain biking.
The three guys together represent a tremendous pedigree- experience, integrity and seperate but respectable viewpoints. Isn't that what the network and the viewers want? Looks like a dream combination to me.