While there is some truth in what you're saying, £300-£3k probably overstates the difference - I think most people would be happier with £700 in economy vs. £1,700 in business if they can get it. It's also a question of how they feel after landing - there's no point in being in Singapore for five days if you feel like you have a hangover for four of them because of your jetlag from economy, when a flight in business could have alleviated that. If that means spending £100 a night on a hotel, rather than £300, then so be it - although £1,700 fares to Singapore are sadly a lot rarer than they used to be.