these are photographers that are trying to build up their destination wedding portfolio, and in order to do so are offering couples a great deal - it's a win-win situation. they may have a great portfolio with "traditional" weddings, but want to work more in the destination wedding arena. i don't think there's anything wrong with this strategy, for either party!
i know a few "established" companies, some of which are on this forum, that have offered contests or other promotions just to get their name and services out there - it's a form of marketing and cost of doing business. in the end, if they get a great referral, then the cost is justified by the increased business. i think it's great that some of htese girls have found a photog that works for them, and is offering a great deal!