I'd argue this point, actually. I'd challenge you to find a character that's as popular as Stitch out of the newest generation of Disney movies (Hercules - Brother Bear). Just like the previous generation (Mermaid - Hunchback), they marketed the heck out of Timon and Pumbaa, who were the most unique and memorable characters out of those movies.
Stitch is the same - for a new generation of kids who's only experiences are movies like Atlantis, Mulan (which I love), Hercules (Which is my second favorite Disney movie), and Lilo & Stitch (my personal favorite - and I'm 27!) - Stitch is the character that stands out to them and who they identify with as a symbol of Disney.
The fab 5 will always be Mickey, Minnie, Donald, Goofy, and Pluto - but it's a challenge for a new generation to identify with these characters, especially when they're hardly ever shown on television. Sure, there's House of Mouse on Disney, but even that is buried between different shows like Kim Possible or Baby Einsteins that kids are more interested in watching.
Stitch is all over the place - TV, movies, DVD, video games - he's their version of what Mickey was for older generations, or what Gargoyles, Gummy Bears, Tale Spin, DuckTales, Rescue Rangers, and Darkwing Duck were for my generation - icons that I love and want to see when I go to the parks. Heck, last time I was at Animal Kingdom and saw a Launchpad McQuack character doing autographs and pictures, I immediately grabbed my wife and made her take a picture of the two of us together.
In 20 years, we'll all be complaining that Zapchar, the star of Disney's newest movie, will be the main focus at the parks, and that he's taking over Space Ranger Spin and making it Zapchars Rip Roarin Blast Fest or something like that. :lol: