Javascript-Only Sites?

[eluser]Vik[/eluser]
It seems like the site I'm developing would be much easier to use if I could do a user interface that requires the visitor to have Javascript. Here's why:

One of my pages will have about 20 popup menus on it. Depending on what the user selects in each one, a new, additional popup menu will appear, with its contents determined by what the user selected in the previous one.

With Javascript, I can (theoretically at least - I'm still working on the code) make this happen.

Without it, I'll have to have a different user interface - one that is more cumbersome for the user.

I looked up how many browsers have Javascript enabled (http://www.upsdell.com/BrowserNews/stat_trends.htm). It seems to be 95%:

Java and JavaScript Trends

This discusses trends in Java and JavaScript usage.
Summary

A significant number of users have browsers in which Java or JavaScript are not enabled. The percentage has decreased somewhat over the years, but it will likely remain significant for years to come.
Recommendation

Java and JavaScript should generally not be used for things which affect a site’s functionality. They are best used to make a site look more attractive.
Details

You can find information about JavaScript, including which browsers support which versions of JavaScript, in Wikipedia.

TheCounter (Jun 2007) reports these levels of support:
[.....]
Users JavaScript Support
5% none/disabled
95% enabled

Sites which need Java or JavaScript to function will deter users who have disabled them, therefore such sites will have more visitors with scripting enabled, but exact percentages likely will depend a lot on the site, and such percentages are not available.

But this quote also says, "JavaScript should generally not be used for things which affect a site’s functionality."

So the question is, with 95% of web browsers using Javascript, why is it a mistake to rely on Javascript for a site's functionality?