>                                             (It is also dropped from CSS 
> 2.1.)

For those unfamiliar with CSS 2.1, having a CSS 2 feature dropped simply
means that there is not a pair of compatible implementations.  CSS 2.1
is not a policy setting document so much as one documenting the status
quo.

It does reflect the very low priority given to structural markup in
commercial browsers, of course.  Failure to get two interoperable
implementation can mean that the specification is techncally flawed,
but quite often means that the feature is not of sufficient commercial
priority.  The whole of XHTML 2 is probably not of great commercial
priority, although DI could be rendered as though it were DL and 
therefore cheaply supported.