There are good reasons to use different font sizes for body text depending on purpose. Hacker News' small fonts fit more comments on the page. A documentation site may benefit from fitting more text on the page. A spreadsheet benefits from even smaller text. The article is easier to read with larger fonts. I tried the article with your rule, it's just not as nice.

Then I changed around my "preferred font size" (chrome://settings/fonts -> Font Size). Blog responds just fine to it. Ironically many, many, many sites don't. It's actually so useless in general to change your default font size that browsers have a much more useful way of letting users have small or large text -- zoom levels.