Basic XHTML prohibitions that I can't understand

Hi,

Can anbody explain why the following elements are forbidden in the XHTML
Basic 1.0 DTD?

* hr (horizontal rule)
* fieldset, legend (form field groups)
* sup, sub (superindices, subindices)

I think they should not be forbidden at all. I understand that mobile
devices may not render some of them properly, I think that is not a
reason for being removed from the DTD. They add important semantic value
and improve accesibility and I don't agree with these eliminations. On the
other hand, I am a "Basic XHTML" supporter (almost all my pages are XHTML
Basic valid and I teach accesibility in the University).

By the way, wouldn't it be great that W3C pages were Basic XHTML valid?
Imagine W3C pages being accessed by mobile devices :-).

Thanks.

Vicente Luque Centeno
Dep. Ingeniería Telemática
Universidad Carlos III de Madrid
http://www.it.uc3m.es/vlc