Len,
You are confusing the specification of the data with the execution of
the specification. It's like saying there'd be some difficulty in
representing a programming language using XML syntax--there's not.
Using a style language is useful for the same reason it is in SGML: I
want to apply different styles to the same basic data objects. Asking
why it's useful here is like asking why you need styles if you have a
font tag and I know we both know the answer to that one.
The fact that the presented result happens, in some presentation styles,
to be interactive is completely irrelevant to the issue of representing
the data using XML.
A better question might be: does XLL (or HyTime event schedules or some
combination thereof) provide anything useful in representing the
relationships among the nodes, which is all an event model does (define
relationships or behavior associated with relationships).
XML only operates at the document representation syntax level, so it can
have nothing to say about the semantics of the data represented. On the
other hand, XLL and HyTime (and DSSSL and XSL) operate at the semantic
level and therefore may have lots to say about the semantics of the data
represented.
Cheers,
E.