To be honest, I don't get the whole economic/networks of production approach that you fellows have been taking to this (it strikes me as irrelevant; the notion of the ability of the Indiana Jones and Star Wars universes to fit into the place-making of the Disney theme parks is what's interesting to me), but if we really want to talk about the associations at work here, Captain Eo, executive produced by Lucas, come on the scene in September of '86.
But if you try to argue from any associations Lucas and Spielberg have with Universal - wouldn't you expect the attractions to be over in those parks, as ET and Back to the Future are/were? As Stoo suggests, playing Six Degrees of Association produces plenty of potential connections that don't necessarily amount to much.
On a fundamental level, it's not just about money. If it were, Disney could easily just get the talent and resources together to build the most spectacular roller coaster possible. The "Disney Connection" is interesting not because of what it reveals about the behind-the-scenes processes, but because it is, as Stoo and others are right to point out, something that does enact some uneasy tensions that confront, above all, one's sense of what these different works and different forms do when they come together. Maybe I'm too quick to throw some of these arguments overboard, but the difference between Mark Twain's inability to approve a Tom Sawyer-themed island and Lucas's and Spielberg's ability to approve the use of their work in various theme parks is not a meaningful one; if anything, it suggests that they themselves perceive their works and Disney to be simpatico.
Edited to add: one interesting avenue for this conversation might be why Disney's acquisition of Marvel is one that truly gives me pause as to the potential future inclusion of such intellectual property in theme parks. Like Stoo, but perhaps for different reasons, it's not a form of storytelling that I find compelling, and the sort of urbanity and particular sort of high octane action and kinetics that would be associated does not fit with either the nostalgic, deep world creations of most of Disney's history-based output (I'd include Indy in this, and perhaps Star Tours too - it's all about place-making - but Frontierland, Main Street, Adventureland, the nations of World Showcase at Epcot are what are exemplified here) nor with the old forward-looking attractions represented by most of the Future World at Epcot product, or an old show like If You Had Wings, that used to exist in Florida - these were presentational, generally not story or place-based. Marvel seems like a dead end, creatively, and one that just doesn't fit. Indy's form of adventure does, though, I still contend.