@iBiscuit - ok i guess i can understand where you are coming from now. Not wishing to go on and on at you, but when you say "Unless all your guests are very well off, I think it's unfair basically to have a wedding where the only accommodation available doesn't suit the guests, in terms of cost or indeed comfort"...I'm not sure that makes sense, with respect.
First of all I don't think OP is in a situation where the only accommodation available won't suit the guests. I think she is concerned that the B & G don't understand the financial consequences of not having a 'full house', and that they are naively assuming everyone will be happy to pay the slightly inflated weekend rates, when that might not be the case.
Secondly I presume you're not really saying that unless ALL the guests are really well off, the B and G should reconsider. That's a bit silly - a wedding invite list typically contains two sides of family, work friends, school friends, uni friends (etc etc etc) and there will almost certainly be people from different backgrounds. You can't seriously be suggesting that the presence of (say) Aunt Lydia and Uncle Alex means a B and G should have their wedding off-peak on a Friday in the city centre near lots of travel lodges and holiday inns, when they really fancied a country manor house on a Saturday, just because Aunt Lydia and Uncle Alex are less well off.
Presumably you mean if someone books a wedding in St Lucia knowing full well that most / all / half of their family and friends can't afford it, that the B and G would be pretty naive Possibly even a little self-absorbed, but i still don't think they're "entitled" unless they start badgering people to attend and throwing a huff when they say they can't.
In any event it would be ridiculous to try and plan a wedding based on what you 'thought' people could afford. Between us DH and I earn £200k and 'own' two properties. But we drive a 15 year old and noisy Peugeot. People decide to spend their money differently. I can afford to go to a spa day at Soho Farm, but if invited I would decline as I would rather have a mini break in Europe.
There's simply no point second guessing what people want to, can or will spend - you should have the wedding you want and can afford, extend invites, and let people manage themselves.