I think almost every bride has had some kind of drama with someone important to them not coming. And while our wedding is the most important thing to US, it is not the most important thing to everyone else, no matter what our relationship is to the person.
My SISTER - my only sibling - did not come to my DW - even with my parents offering to pay for her entire trip - she didn't want to leave her husband with their kids for the weekend. To me, that was very hurtful - she told me that she and her husband didn't have the money to come, yet since then they've gotten a dog and done countless other things that have added up to much more than they would have spent on our wedding - especially with my parents paying. I cried a lot about it - cried to my parents, to my FI/now husband and to her, but it didn't matter. I think she just didn't want to come and that was it.
By the time the wedding came, I decided to just say F***K it - she will be the one to regret not coming - we had an amazing time and an awesome wedding - everyone had a great time for the whole time they were there. she is the one that missed out - she will never be able to make that up.
Getting mad at the people that say no only gets you upset - they've made up their mind - they are the ones that miss out and have regrets when they hear about it and see the pictures.