OK, this is weird. I think there may be quality differences between the early AT101Ws and later ones. I have a beige one I bought used from Clickykeyboards a while back, made in Mexico, model number GYUM90SK, Rev A00. And I have the beige ones I bought nib on eBay a couple of months ago, made in Malaysia, same model number, Rev A01. The one made in Mexico lacks the strain-relief block on the cord, but is otherwise visually identical. But the keys on the Mexico-made board seem more precisely seated and sound less clicky (but not like the SGI AT-101s). Most noticeably, the space bar on the Mex one does not rattle at all, as all the Malaysian ones do by comparison. The Mexico-made one is much nicer to type on, with less of that "plastic" sound.
What's weird is that the black one I bought nib is made in Malaysia but also seems more solid than the beige Malaysian ones.