When I called, I was told to also send e-mail to:
disneyinfo@disneyhelp.com
if you want a direct e-mail address instead of a web form to fill out.
When you contact Disney, remember:
* Be polite. You're less likely to be taken seriously if you rant, insult, swear, etc. Just be firm about your disappointement, explain what you want, and why you want it.
* Mention specific titles (in this case, Muppet Treasure Island and Muppet Christmas Carol) that you will not buy because they are not widescreen. After that, you can mention that you won't buy other Disney titles that aren't in their original theatrical presentation either.
* If you've got a kid, be sure to mention that; Disney's supposed angle on this is that these are "family" films and "families" don't like black bars caused by widescreen.
Hope this helps!