Isn't the marquee tag a propriety tag, though? If I'm not mistaken, it would only work on IE based browsers.

If I were to categorize the languages you mentioned, this is how I would do it:
+ Markup languages +
- XHTML
- XML

+ Dynamic +
- Server side -
-- PHP
-- ASP
- Client side -
-- JavaScript
+ Querying languages +
- MySQL

Each of these categories are meant to do different things specifically so it would be wrong to generally compare one category with the other.

XHTML is the new HTML. HTML became a very messy language, very different from what it was inteded to be.
Initially, all SGML (Standard Generalized Markup Language; X/HTML is a sub-class of this) branches was mostly meant to hold data in an organized manner, that is why there are all those header tags, and div tags and paragraph tags, etc. But during the browser wars, in order to make their browsers "better" they introduced various styling elements like <b>, <i>, etc. All of them style the page but don't have a semantic meaning. This is why you're supposed to use CSS instead of formatting tags because X/HTML is meant to only hold data in an organized manner.

I don't know how much further X/HTML can go...but with CSS3, we should be able to do some pretty cool things but nothing dynamic really sicne X/HTML isn't meant for that.