Where to draw the line between structure and presentation?

Not many people will argue that a table is a structural element of a graphic interface. Tabular data is meant to be presented as such. A desktop web browser, your $700 phone and links will render tables as is. Why is then relative container position not considered structure, but presentation?

You can't make a two column web page without using CSS (unless, of course, you use tables). Wouldn't it be weird if your desktop applications placed the Add button under the text box when you need it to be next to the box? Does it make sense to browse the web on links and having to scroll down at least three pages to get to the content because the super long left sidebar is rendered before the actual content?

Would adding layout elements like as position and size properties to the structure language of a GUI really make things less orthogonal? I'm not saying you should allow style attributes on GTK+, but it makes no sense that web documents use CSS for layout. You can browse the web without colors or special fonts, though usability is affected when you break the layout the original author had in mind. Not sure whether I'm missing an important design detail or the web is being an unorthodox hacked-together piece of shit as usual.

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It's impossible not to write CSS when you need a sidebar, even if it's just a plain colorless sidebar. Positioning is structure, not presentation. The web has it wrong.