Correct, Cleartype was NOT the default in Windows XP.
If I recall correctly, it wasn't "unsmoothed" either, but - indeed - "standard font smoothing".
I am in Linux right now, so I don't see the settings dialogue of Windows XP.
But it is something like this:
Open the display properties dialogue, go to "effects" (if that is the right term), you will find a setting with a check mark; if you remove the check mark, unsmoothed rendering will be the result.
If you leave the check mark, the stock setting is "standard font smoothing" (or whatever it is called precisely), you may, however, change this to "Cleartype" - which is not the default in (at least) XP (don't know about Vista, 7 etc.).
I am aware (from hearing about it on the Internet and also in this thread, for sure) that there are users who like or want Cleartype.
Our eyes must be different, though, because I absolutely can't stand it (whatever settings in the tuner) - seeing coloured subpixels is just unbearable to me. In Linux, it is even worse for me: I cannot stand subpixel rendering and I cannot stand grayscale there - so I am forced to use jaggy unsmoothed rendering.
Of course, one can use hardware based rendering in Firefox (for instance in Windows 7), but whether I use it with Cleartype or with standard font smoothing, any directwrite rendering is too blurry for me.
Partly, all this may be a matter of preference and taste, but for some it is more than that:
a matter of doing harm to one's eyes and health or not.
-egman-