GAH, not that lie again... Well, more a lie by omission. See, that little bit of math is so flawed you cannot/should not rely on it for building a page -- ever. Seriously I meet whoever started advocating that in a back-alley bad things will happen. More typical idiocy started by people who failed to grasp how things work under the hood.
See, not all computers have 16px as their default font size, as that 16px default is/should actually be declared as 12pt... Yes, PT. IE and Opera both traditionally treat their default font size as such just like all other good little doobie windows programs... because Windows lets you change the "system metric"
So what is a "system metric"? Basically it's a dpi setting for your display. Just as you can change the resolution of your screen, you can also change the dpi setting for font and application rendering. The generic default settings on most computers is 96dpi... But windows has had the option to switch to 120dpi pretty much since Windows 3.0! This means that instead of a 16px default font in browsers, you SHOULD get 20px... which throws that 62.5% nonsense into havoc as it ends up being 12 or 13px (depending on browser rounding) instead of 10px.
That's the ENTIRE REASON for using %/EM, so that it is based off the DEFAULT font which is NOT A FIXED SIZE. That is also WHY PX is a miserable fail at accessibility. As a Large font/120dpi user if I have to dive for the zoom, there is something wrong with the site I'm visiting!!!
Some handhelds render at 72dpi... some desktops render as high as 192dpi... Windows has let you set any dpi you want since Win9x, with the two standard sizes of 96 and 120 as the 'default choices' -- Win7 now offers four default choices -- small (96), medium (120), large (144) and extra-large (192)... and the browser SHOULD obey that. (though Gecko and Webkit do not... Opera and IE do/can). Even in browsers that don't obey it automatically, you can manually change the default font size!
I made a page a while back to show all the different behaviors of the different browsers when fed all the different font metrics.
Effect of Font Metrics on Common Sizes
pay particular attention to the behavior of %/EM and PT on 120dpi systems in IE/Opera compared to 96dpi ones.
This also where that article has a massive flaw -- even though it too is popular misinformation. See, PT is NOT fixed, no matter how you color it. How can I say that? Simple, it's relationship to dots is not fixed!!! Where people get the idea that PT is a fixed measurement is beyond me -- because it flat out isn't in relationship to screen pixels or print dots!!!
A pixel/dot is a fixed hardware measurement -- it's the smallest real unit the physical device can make. This is WHY resizing "pixels" actually makes NO SENSE WHATSOEVER!!! I'm actually with old-school IE on this one -- px fonts should not be resized -- unless as Opera introduced and STILL does better than anyone else you resize ALL elements that are declared in PX!
PT is a measurement based off inches... so if the number of dots/pixels per inch changes, the number of dots/pixels per PT changes. Look at that page of mine -- at 96dpi you end up with 12pt equalling 16px; at 120dpi 12pt equals 20px.... at 1200 dpi high quality print, 12pt = 200px!!!
It's why for a long time developers used PT on sites, and it was THE choice for forum skins right up until around 2003 -- it was the only measurement that automatically adjusted to the system metric in all browsers (even nyetscape/gecko obeys PT auto-sizing). It's also why I was slow to adopt %/em because I didn't want netscape/gecko users to have to dive for the zoom in the first place!
I've changed my tune on that now, because I've realized that accessibility and Gecko or Webkit is such a joke because they LITERALLY believe all machines are 96dpi (as several webkit devs have run their mouths about in the past) so much like everything else accessibility related in those browsers -- it's a total joke... much like geckotards clinging for dear life to the resizing of text like the sweetly retarded cousin of nyetscape 4 that it is, accessibility in those browsers is a bigger joke than it is in IE... So screw 'em, %/em for content areas it is. It also doesn't help that Opera 10+ no longer obeys the system metric on PT, even though it checks the system metric and does set the default size to 20px on large font/windows systems (bizarre)
Though I see little wrong with px for areas where image interactions force you into it for layout reasons -- assuming it's small things like buttons, controls or narrow fixed columns, so long as you keep in mind that anything below 12px is illegible for large font/120dpi users, and I personally wouldn't go below 14px unless you do all uppercase on that. (add 2px more for serif fonts!)
Case in point, these forums, where the text entry boxes and posts are all a nice big easy font with my 120dpi setting, but the text on areas like "send trackbacks to" or the labels next to the checkboxes under "miscellaneous options" is uselessly small to the point I have to zoom 50% to even read them -- all because they're declared as a uselessly small 11px (for christmas only knows what reason).... Well, zoom or move my head to a foot and a half from the display instead of the comfortable 2 and a half to 3 feet I usually sit at.
Though that's why I run a user.css here in Opera to override all the font sizes into something USABLE. (even if it does screw up the layout slightly).
Still, if I have to zoom a layout just to read it as a 120dpi user, I have the overwhelming urge to pimp-slap whoever wrote the page, as there's no excuse for it apart from ignorance... or letting the "but I can do it in photoshop" nimrods have their way with pissing all over accessibility.