The real difference between Broad’s case and that of Clarke and Haddin is that Broad wasn't given out. The umpire got it wrong and there was no correction. This is not a failure of DRS or the system. It is a failure by Clarke who used his two referrals unwisely. DRS is supposed to be to stop really bad decisions but it cannot do that if someone tries to use it tactically and gamble with it. As with all gambling there will be losers.
I have heard the argument “let’s just have one referral, that way it will only get used for the really bad decisions”. This seems flawed because once the first referral is used up there is only one left. So any side that uses one referral has automatically trialed only having one. It didn't work then.
I think the DRS works well as it is – we just need captains that know how to use it.