I have heard of this, and would say that it is the norm.
I would definately question the bride by asking "why can't we choose a different resort", if the response was "so I (as the bride) can save $ per plate", my honest answer would be ok, then we'll kindly decline the invite.
If you cannot afford to cover the cost of your guests -- whether at an at home wedding or a destination, then you should rethink your choice, or drum down the guest list. It really is simple.
In a sense this relates back to 'at home non-DW brides' having an expectation that if each plate costs $x, then the gifts from guests should at least cover the per plate cost, this simply is not the case.
Weddings are about having the celebration you want, with the people you want, in a capacity that the bride and groom can afford. With no expectation of 'coming out ahead'.
Sorry if this is harsh, but I truly believe it is a reality.