I don't really think you need a special occasion to visit any Disney park. The visit itself feels like a celebration to me every time I have gone. But, there's nothing like bringing the family together to celebrate a special anniversary, birthday, or anything else worthy of commemorating.
I get why someone would have their wedding there. I've celebrated my birthday, and my son's birthday there and the experience has been so special...so, er, magical, that we have decided to celebrate at least one birthday for each member of our family there.
The service from everyone at the resorts and parks truly helps you make whatever the celebration all that it can be.