My observations suggest it's a national thing rather than specific to Disney fans. I find many more American's who won't fly than I do Brits or other nations.
In my opinion, and experience, the answer is simple. Europeans travel abroad much more than Americans do. There are a number of reasons for this, not the least of which is the tremendous landmass that is the United States. If you're going to go somewhere in the UK (as on holiday), chances are you're going to HAVE TO take a plane unless you're not in a hurry and take a boat.