I want to believe that the people behind it didn't bother to test it on different viewports, but I have created websites that look fine on everything from iPhones to large monitors without writing viewport-specific CSS.
It just seems incredibly sloppy, which is hard to believe for a company like ALA.
Just checking, but really "look fine on everything", or "need to be zoomed in by many people"?
Of course, those have been very sparse in layout such as blogs, so it's not a solution that fits all, but in a case like this, it would work just as well.
A site like Hacker News obviously needs optimization for different viewports.
It's pleasing to be in a situation where I can say (about ALA5.0) "you can zoom out, if you want, of course" :p
100%/16px is standard for article body copy.
The main part of the article, set at 18px with about 700px width, is sensible IMHO.