I didn't downvote you but I personally never worry about users with JavaScript disabled, and the companies I have worked for don't care either. The number of people without JavaScript is most likely way to low to spend time on an HTML fallback.
An adequate "fallback" is <noscript><p class='something_nice'>This site requires Javascript to function</p></noscript>. It's not exactly hard, and it's better than a blank white page.
It can also occur due to network problems on occasion or other technical issues; if you have JS beyond just progressive enhancement on your site you really ought to have a <noscript> tag in there somewhere.
It's a fair argument that overall percentage is low, but if you are catering towards a more technical audience (submitting to HN would count as that in my books) then I imagine the % of those using some form of Javascript blocking software is much higher.
Plus as mentioned, it isn't like it takes much effort, a noscript tag and a paragraph saying that it is a pure JS web app/what it does is enough.
http://www.quora.com/What-percentage-of-Internet-users-use-J...