Agreed partially, Broadcasters Like Sky Sports have their own shows for almost all Cricket Action telecasted by them, Likes of Nasser Hussain would prefer to work there.
Also Agreed that BCCI has its own norms regarding commentary, Although, For The IPL I think Star And BCCI would have some Mutual understanding regarding all aspects.
There are 3 types of Contracts,
1 is Exclusive Contract like Akash Chopra has with Star, Bob Willis has with Sky UK, where you can not have any Commentary stint with rival Broadcasters like SPN, D Sports, BT Sports etc. Even if there is no live assignment with existing Broadcaster.
2 is Preferential Contract or long term Contract if 2 Events are happening then Commentator cannot walk over his long term Contract for short term gains.....
Sky Sports UK has Mike Atherton, Nasser Hussain, David Lloyd, Ian Botham, Michael Holding
Channel Nine has with Mark Nicholas, Ian Chappell, Mark Taylor, Ian Healy
Super Sports South Africa has with Mike Haysman
Sky Sports New Zealand has with Ian Smith......
But they do Commentary Assignments with other Broadcaster if that is not competing with Long term Contract like Nasser Hussain, David Lloyd do for ICC and Host Broadcasters if England tour other Countries.... Michael Holding and Mark Nicholas is doing Commentary on Super Sports for current SA Vs Aus Test Series.
3 is Series Specific Contracts where Commentators like Sanjay Manjerakar have Contracts for individual Series.....