> Is made up of table tags, which the CSS people will tell you is wrong/impossible/has different semantics

A table is a grid. Lot of UI toolkits have a grid container, and even CSS added it specifically as a layout engine.

> A table is a grid. Lot of UI toolkits have a grid container

Sure. As long as the end result is the same grid, it shouldn't matter. But in a CSS world you switch your table for grid-layout divs (or vice versa) and suddenly one corner case thing that is in one grid cell somewhere in your app gets its styling flipped.