As I said in the title, isn't TeX "similar" to static web pages? Can you accomplish the same things with both, or is TeX limited to words?
Why would one prefer HTML and CSS over TeX, or vice versa?
However, in principle these things could be arranged by the author, if – and that is a strong ‘if’ – one were writing for only one interpretation of one browser with a certain font.
HTML alone is (theoretically) much stronger in the semantic interpretation of data than is tex, but this is not relevant for the typographic representation. (It is of course indirectly connected to the representation by typographic conventions.)
Still, it is really complicated to produce cross-browser and cross-system compliant documents this way, which is one reason that no such complicated framework has evolved yet. (Another reason is that it is not needed that badly.)
*: One feature which is hard to add, is proper font support on the scripting level. With current techniques, it is especially hard to get e.g. kerning information or OTF glyphs out of the font files – all of that is being handled by the browser and even the most advanced and specialised web design will need to rely on the browser’s mapping between unicode character and OTF glyph. This will most probably change at some point in the future as the typographic techniques converge. (See: http://hacks.mozilla.org/2010/11/firefox-4-font-feature-support/ )
No. You have pretty much no control over how pages break with HTML+CSS (or if you have, please share how). Besides, you are comparing apples to oranges: TeX is a typesetting system, HTML+CSS isn't.
TeX is a Turing complete programming language. I haven't seen any browser plugins yet written only using HTML and CSS. There are hundreds of from small till giant packages for (La)TeX, like PSTricks and TikZ. Ok, you could draw your vector graphics with SGML, but please compare the code required for that and e.g.
TeX includes algorithm for line and page breaking and HTML+CSS does not. Compare a PDF produced with DocBookXML compiled with Apache FOP to PDF, or simply a website printed to PDF and one made using LaTeX, then you can see the difference in typesetting quality.
TeX allows for automatically generation of e.g. table of contents and other lists. This doesn't work with HTML+CSS out-of-the-box. Same counts for references and citations.