Just to confirm that the author of that article really is llasram (whom I haven't heard from in a while).
It is certainly true that MOBI is currently a more "stable" platform for which to create ebooks. It's much easier to take random HTML and convert it to a MOBI e-book that will work than an EPUB e-book that will work. The price you pay for that is lowered fidelity.
However, I think the problem with EPUB is simply that of growing pains. Supporting CSS 2.1 means that EPUB renderers must load entire XHTML flows. This in turn means that EPUB creation software must impose some sort of limit on XHTML file sizes. As people get used to that, not working EPUB files will become less common. After EPUB is still very young.
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