True, but no one wins if the user leaves your website frustrated. Gracefully degrading in absence of a full-fledged scriptable web browser should be considered best practice.
Graceful degredation is definitely a plan.
Now look at it this way: The Wayback Machine is probably the most prominent part of the Internet Archive. Does it handle websites that rely on Javascript?
Accessibility and USA law: http://warc.calpoly.edu/building/page_design/javascript.html
I agree with all of your other concerns, but it is not the responsibility of the web designer to accommodate people who selectively disable parts of their website. If you turn off CSS, or the color blue, your experience will degrade, but that's 100% your fault. The same is true with javascript.
It runs quite well on my 1.8ghz Atom netbook and my Nexus 5. The JS they're using doesn't seem that expensive.