Simpsons are also shot on film or at least the earlier seasons were, which makes it no different than Snow White (other than the production cost) when it comes to HD rendering. In the past 10 years or so they developed digital HD cameras which film in high definition unlike movies filmed prior to that. One of the earliest examples of films being filmed in the HD format is Star Wars Attack of the Clones. That being said, theres a common misconception that these are the only things that can truly benefit from being in HD and not things that are rendered into HD after the fact like films prior to the new digital filming craze. Point being, anything if rendered correctly, will look improved in HD. Even if its just slightly crisper lines and black definition which would be the Simpsons ink and paint era rendered for HD.