Walt Disney's original intentions in designing a magic kingdom were to create a world where children and their parents could have fun together. Yes, that's what Disney World seems to be, even to the extent that all ages enjoy it, with or without children - and that is why people keep coming back. They started with one man's dream and then built upon it.
Like others have said though, just because it's a fun, enjoyable place to spend time doesn't mean that it can't be educational. It can be as educational as you want it to be. And, IMHO, the educational aspects of Disney World are the best forms of education. It's not in-your-face education like a lecture or a museum with a bunch of informational signs to read... it's educational in a non-direct way. Fun experiences - memorable ones - can teach us plenty that we will never forget, as Disney imagineers help us to become completely immersed in new worlds. The sounds, the sights, the people, the interactive experiences... try getting that from a classroom textbook!