The real win is application independence as you note. Beside that,
conversion from SGML tends to be easier than converting *to* SGML, so
one can generally buy a great amount of flexibility by using SGML
technology. In Novells' case, they can use the same data (different
stylesheets) to publish online documentation, or CDROMs (in fact, with
Dyna*, it's the same (compiled) sgml database file even).
Once SGML databases become mainstream technology, things will look
even better. The real painful part of SGML is in the nature of the
object representation, which disallows easy manipulation of single
objects. Once that barrier is overcome, document creation and
manipulation will undergo a slow, but profound change.