That little tidbit of info doesn't really justify this post's headline. Read on:
Pre-2009, pulling something like this off would have been a licensing nightmare, to get these two huge companies and play nice and figure out how to share their money and intelectual property. It's not now, because they're all one company, but that doesn't mean Disney hasn't done a couple things similar to that.
The most recent example, "Wreck It Ralph," see its antagonist Ralph escape his fictitious videogame Fix-It Felix Jr., where he is unhappy with his role as the game's villain to explore a world made up by many video games, some of them familiar, like Pac Man, Sonic the Hedgehog and Super Mario Bros., some of them made up, like Hero's Duty and Sugar Rush.
The only character from Super Mario Bros. that's included is the second-tier character Bowser, because Disney didn't want to pay the royalty fees requested by Nintendo. Not surprising, since out of the three games mentioned, Super Mario Bros. is the only game that managed to stay current (excluding iOS apps).
I was born a few of years after the most daring feat of cross-branding animation feature "Who Framed Roger Rabbit" was released, and grew up watching what turned out to be the kickstart of the Disney Renaissance. As a young child, seeing Bugs Bunny and Mickey Mouse in the same movie makes sense. They're both animated, why wouldn't they exist in the same world?
As seen through the eyes of any person of any age, it still makes sense. That's why these cross-branding licensing nightmares are dreams come true for audiences. If Wreck it Ralph escaped Fix-It Felix Jr. to explore the internal world of video games, it would only make sense that he ran into Sonic and Bowser. Anything else would seem like cheap pandering. And if Donald Duck was a real, living being, when he got off work, it's completely plausible that he could be neighbors with Daffy Duck.
As adults, it is also known what a legal feat it is to get these huge companies together to do something like this, adding to the wonder of it all.
It only works in films though: in the physical world, I like to keep my Animal Kingdom and my "Avatar" separate.