I can see what you mean, but I can also see why Adobe chose this path. A pure CSS solution may offer the ability to simply define an array of boxes for the content to flow through. On the other hand the css box model requires html elements in the hierarchy to attach to, in order to manage the cascading aspect of css.
I agree, it is a sticky problem. Really, it does make sense to have the content areas defined by divs (though what to do if one of them ends up empty?) And once you've done that, where is the content supposed to go? I suppose then it makes sense for it to be in a separate hidden div... What happens to styles put on that div? Will the content div be represented in the DOM? I feel like it makes for some sticky questions.
Before this proposal, you might have attempted to implement these features server side; deciding what parts of which text should end up in each div. It's just unclear to me that having this hidden div is the best way to bring your text up to the browser.
Still, if by using that, you're implying a pseudo class or something like #container:first-column and so on, there's risk of having a mismatch with regards to the number of columns defined on the parent.
