From what I understand the default font size in most browsers is 16px.
If you're using IE on Windows XP with 96dpi set and no changes to anything... seriously even though most of my browsers are set somewhere around the equivalent of 16px, I'm running Gnome Desktop which makes everything in Firefox bigger compared to Win/96dpi meaning text will wrap over here where it doesn't on the dev's Winblows machine.
And then you have the font... did you set Verdana? Georgia? Larger x-height than say Arial or Times New Roman. And I get to set that in my browser, you only get to suggest it : )
In any case you obviously aren't running the default something. Weird screen rez, weird font, weird dpi, weird browser. Like most of us : )
Why one is better off setting font-size on the body to 100%. The whole 62.5% idea needs everyone to have the same dpi and default font setting. Something as unreliable as the chances of my sock colours matching.
My issue is when I set the font-size for the body to 62.5% the text is super small but when I set it to 10px it is bigger.
Now you know how we all feel when trying to actually read something on all those sites who took that Truth as Gospel (too bad it was pushed by some big names in web developement... like Dan Cedarholm and others... people who we trust because they Know web design). This is why it's not recommended to do 62.5%... you do want to use a % though, on the body, to get around an IE resize bug.