That doesn't mean that LaTeX is worthless on the web. The gluing algorithms that Knuth used for creating sentences and paragraphs do (for the most part) work, even in documents without pages. In all honesty, the web could benefit greatly from LaTeX, pagination aside.
I'm glad that the author seems to have a practical perspective on this: >We think LaTeX is still the best programming language to tell a computer how to place text on a page. But the TeX project started pre-web, in 1978, and its scope and function are tightly linked to the printed page, not the webpage.
He goes on to give an example of constructing a table in LaTex which requires (or assumes by default) a suggested location for LaTeX to place the table in the page; something which is currently nonsensical in all but a few web environments. Like the author, I also find CSS appealing for a potential "LaTeX" on the web solution.
However, LaTeX was designed from the very first to be the next standard in type setting and is a turing complete language. CSS is still under debate for being turing complete, and it lacks nearly all of the features that are iconic of LaTeX, except for the ability to format math equations ( and even then...).
I'm not sure what the next standard in typesetting will be, but it will be designed to be device agnostic (with book existing as a supported format), it will target the web and similar digital media, it will be turing complete, and it will be created specifically to fulfill each of those goals, not to have them retroactively attached in a ham-fisted way.