>While I'm in the camp of `font-family: serif/sans-serif`, this paragraph strikes me as strange. If you choose a font for your own content on your own website, why would you choose something that doesn't contain all the characters you need?
Once the site is choosing their own font you are probably relying on non-domain experts to do the choosing of the font, probably a developer or designer. These people sometimes will think it works on my system on the language I have tested it on and not think off hand but does it work with all the characters that need to be supported. Thus when your site chooses not widely available fonts or builds their own fonts this is a potential source of bugs.
Once the site is choosing their own font you are probably relying on non-domain experts to do the choosing of the font, probably a developer or designer. These people sometimes will think it works on my system on the language I have tested it on and not think off hand but does it work with all the characters that need to be supported. Thus when your site chooses not widely available fonts or builds their own fonts this is a potential source of bugs.