They were discussing this on the South Africa broadcast, HotSpot's an expensive piece of equipment, that's why only 2 of the TV companies in the world currently use it, those being Channel Nine in Australia and Sky Sports in the UK. It's just not financially viable for every TV station in the world to pay for this technology, meaning if they were to implement it into the referral system, the system would only be in full use in 2 countries.
I like the referral system at the minute, it may be a little slow, but it's in the early days of use. I do think the umpires should be able to use the predictive hawkeye, it's 99% accurate, so shouldn't be used as the only basis to give a batsman out, but it should be used to assist the umpire in making a decision, as ultimately we're looking to make as many correct decisions as possible.