Overall it is, but when the above commenter mentions box-and-glue, they're talking about the building blocks of the line breaking algorithm TeX uses (you can read about it in this paper: http://onlinelibrary.wiley.com/doi/10.1002/spe.4380111102/ab... ). The box-and-glue system is a way of expressing a layout as an optimization problem (in the paper, they talk mostly about determining line breaks within a paragraph, but the idea of minimizing badness can be extended to determining page breaks as well). A bigger concern for me is the performance of laying out any reasonably complex page — the performance we get from rendering a reasonably complex webpage today is generally much better than rendering a reasonably complex LaTeX document.
I've come across a feature request for Firefox where someone proposed to use the Knuth Plass line breaking algorithm just for text layout, but they didn't get very much traction: https://bugzilla.mozilla.org/show_bug.cgi?id=630181
Are there any CSS replacement proposals that are based on linear programming [1]? There are a lot of things you cannot solve with just LP (e.g. rearranging floats on a page) but it's a pretty good -- and simple -- abstraction for laying out boxes relative to each other.
Solving LP is fast, especially when many of your constraints are equality constraints (as would be when specifying tables).
I think Cassowary [1] is what you're talking about (particularly section 1.2 where they talk about some modifications to make their system very fast for incremental updates). Apple has based their constraint-based layout system, Autolayout [2], on Cassowary. There's also a project that incorporates Cassowary constraints into a CSS-like declarative syntax called GSS [3].
I've come across a feature request for Firefox where someone proposed to use the Knuth Plass line breaking algorithm just for text layout, but they didn't get very much traction: https://bugzilla.mozilla.org/show_bug.cgi?id=630181