Funny you say that because i find the font size used by that site to be the most comfortable for me (and i have far from a good sight...) and i really dislike sites that use huge letters (like f.e. Medium). Then again, i prefer small font sizes in general and i dislike the tendency to waste space in modern UIs - both web-based and desktop (and mobile, but i don't use that much and in mobile it is kinda of acceptable because fingers - although i'd really like it if mobiles came with a stylus instead and adjusted their UIs accordingly).