Yeah, you’re right. I’m foggy on the dates of what was released when for Disney, but I was thinking more of the TV shows than the movies. Like the Mickey Mouse, Donald Duck, etc. cartoons I watched as a kid, but they could be from 1930 and have been replayed for 60 years, heh. Comparing Peter Pan (a full blown movie production) with like, Speed Racer (a cheap TV series) isn’t really a fair comparison, you know? In comparing movies, you’d have to compare like, Ghost in the Shell or Akira with something done by Disney around the same time (101 Dalmations? I’m not sure how old GitS/Akira are). Most of the listed shows (Speed Racer, Kimba, Voltron, Robotech, and Starblazers) are (I haven’t seen Kimba or Starblazers, so I don’t know for sure about those) TV series. 
The half-hour shows (possibly even stuff as new as Tail Spin and Darkwing Duck, it’s been a few years since I’ve seen them so I could be wrong, and ignore all this if I am, heh) all used flat colors (like a beak is orange…whereas in anime you’d have orange, a dark orange for shadows, and a highlight as well). Once Batman: The Animated Series came out with actual shading, everyone seemed to pick it up from there (Gargoyles is the one that stands out most in my mind as helping start the big wave of “hey, let’s start shading”).
Again, I’m fairly foggy on the dates of all this, heh…Bugs Bunny and the other Warner Brothers shows used flat shading as well (quickly found a site that sells cels, and found a 1984 cel of Bugs/Fudd that use flat shading). They moved smoother than anime, but the time put into each cel was probably significantly less.
Now people are moving into airbrush shaded cartoons…bleh, I hope that doesn’t catch on too much. I can’t stand it, heh. I don’t have anything against flat shading, because the smoothness of the movement is a nice trade-off (it it was choppy like anime AND flat shaded, I’d be irritated…like Hammerman, heheh), but smoothness isn’t everything. 
- Tsugumo (I think I’m using “flat shading” and “flat coloring” interchangably here, heh…I don’t know the real terms for it so I’m winging it)