A markup language, by definition, cannot define behaviour. You can do design, layout and animations with markup, but you simply cannot do any kind of processing or behaviour (when I say behaviour, I mean things like authentication, processing, manipulating data, etc). So if your webapp needs to be behaviour-rich (which I don't know how you can call it a webapp if it isn't) then you're going to need a scripting language to define those behaviours.
HTML + CSS + JavaScript are complex tools, it would be great if we could unify them into a single language. I think that jQuery's success is in part due to this unification, but I certainly don't think jQuery is the answer.
Lispers have said a few times that HTML/Javascript would be well replaced by S-expresssions and (a) Lisp. There are more than a few reasons why it won't catch on, of course, but even to an old-school imperative programmer like me it sounds a damn sight better than what we have now.
HTML + CSS + JavaScript are complex tools, it would be great if we could unify them into a single language. I think that jQuery's success is in part due to this unification, but I certainly don't think jQuery is the answer.