I think all one can expect from a close friend (or family member) is that theyconsider the invitation carefully. Putting some effort in to determine what is possible (checking finances, leave accrued, etc). A couple cannot expect anyone, really, to go to a destination wedding - if it is not possible due to any one of the many possible reasons, that make a trip impossible.
We got married last year - half of our bridal party was from interstate - but I knew that I really, absolutely wanted them there if they could manage it - so we budgeted from the get go, to contribute to flights, accommodation, making things financially viable for them all to attend (out of the 40 people, 10 were bridal party/ushers - and the other 30 were family). As well as contributing, we spoke with almost everyone we invited (during the planning stages), to ensure there weren't likely to be any major clashes, or people missing (for instance, if my brother had something else on, that would have knocked out 5 of the people we wanted there the most)...I don't think that's necessary for all people, on all occasions - but I feel like you did everything you could to outline what would be possible, and what would not. You did everything right.
I can understand the disappointment your friends are feeling - but that's not on your head.
I hope DF and his Best Man manage to speak directly and sort something out. I would avoid talking to the wife about it if at all possible - sounds like she's having a bit of fun keeping you guessing!