I've travelled all over the world, and I've done many trips to WDW (and other Disney parks - Paris and Cali).
I loved seeing the Pyramids at Gizeh, the Acropolis in Athens, the Buddha on Lantau, the Forbidden City, Piccadilly Circus, etc etc etc...
But I also love going back to the safe, predictable and most importantly FUN Walt Disney World. I don't have to worry about getting robbed at knifepoint (except in that bad neck of the woods near IASW...heh). I don't have to reconsider ice in my drink, if the fruit has a peel or if that 'chicken' is really chicken.
As for the primary features, the parks and attractions, well, very few other theme parks can even compare. Yes, I wish WDW had a comparable to Spiderman or MIB (yes, yes Midway coming soon), but for the most part, the attractions are just so unique (okay, maybe not the 'Dumbo'-class attractions...).
And the proximity of things that are normally scattered across my home city...restaurants like Whispering Canyon (that are anything but), mini-golf, bars (lounges) with atmosphere that don't always just play boom-chicky-boom music (which is great for dancing, but not necessary ALL the time), or plenty of unique shopping.
99 holes of golf - not bad, but there's more than that with a very short drive from my office. However, none have a Mickey shaped bunker...
The monorail - that's pretty slick to ride, but it's not unique. Other cities have them...hmmmm the ones in Las Vegas look awfully familiar.
In a roundabout way, what I am getting to is that the synergy of all of these elements, a fusion into one whole, is the real draw, at least for me. Disney merges a variety of elements - some extraordinary, some mundane - into a single entity. When you experience THAT seamlessly, there isn't a lot of room for real world stuff.
And that's why it can compete with travels abroad...