The default text size in every browser, as far as I'm aware, is actually 16px. The text on Hacker News is 12px, because virtually every designer decides they know better than the browser settings.
Which one are you thinking of as the "default"?
Which one are you thinking of as the "default"?
And yes, HN itself is smaller than that.
"Designers" hate this because they can't massage every pixel into just the right location on their cinema display and can't be bothered to accommodate different hardware. They'd rather just send users 300 DPI images of everything and let the proles deal with downsampling them on their ever so inadequate devices.