@cybershot I think the confusion is due to it being considered abnormal behavior, which it is not. Sure, it doesn’t equate to leading in print design, but that is how it is specified (http://www.w3.org/TR/CSS2/visudet.html#line-height):
Still for each glyph, determine the leading L to add, where L = ‘line-height’ – AD. Half the leading is added above A and the other half below D, giving the glyph and its leading a total height above the baseline of A’ = A + L/2 and a total depth of D’ = D + L/2.
So in layman’s terms: If there is a positive difference between the capital height of the type, and the line-height, that difference is split in half, of which each half is placed above and below each line of type.