I havent even formalized my wedding plans and I am finding myself in this situation, with my parents!
I guess with all their excitement with the engagement and beginning stages of the planning that they are telling everyone, and think it is ok to extend the invite! We have gotten into a few heated discussions about how this is our wedding, and we have previously agreed that we do not want any guests who we do not have a personal relationship with. One of the reasons we want to do a DW is because if we stayed here we would have to invite people that neither of us knew. Plus, like many others have mentioned, I dont think they fully comprehend that the wedding is not free. Hopefully now that we have discussed the issue at length they wont be inviting any one else.