I get you. I think you're right - if you have a page which does make heavy use of JS, it can be difficult if not.impossible to replicate the same behaviour without it. HOWEVER: you can often get something close enough!
To go back to my shop example: yes, you can use JS to show a richer shopping experience, with pop-up windows, filtering, and the ability to add to cart without leaving the page. Graceful degradation would be to show the same listings, but without the more convenient features that use JS - so without popups, with filtering that refreshes the page, and a completely separate cart.
Some apps really can't function without JS, because they are... well, apps.
People do stuff in JavaScript that you really don't need JavaScript for. You don't need JS to display a store listing, for instance. Or a news page, or documentation, or even a search engine
Watership Down