Simple markup and baroque styles is also more mallable, something that matters most in the field where I spend most of my time, between device independence (device is most of the time Opera-speak for phone), accessibility, and multimodality (which in Opera most of the time means Voice). They all have similar, but not identical, requirements, there are even a few features that would be a boon for one group of users but detrimental for others.
Any web designer that cares enough to test for every possible user group in every possible situation would probably not have time to do any web design, and neither should he have to. The good news is that most of the good habits are easier than than the bad ones. It is easier to mark up a headline than to specify that this paragraph has a 'b' element and a 'font' element. But before general CSS support the headlines were unpredictable, and tools still reflect that. CNN for instance has specified one headline on each page, which is patently not true.
Joe Clark has in A List Apart written an article on zoom users and Small-screen rendering. Opera has both, but with a separate origin and use case. Accessibility as defined by WAI doesn't include the access problems a phone user might have with a web site and that is reasonable. It isn't their problem, most in the community have a hard time using a phone at all except for phone calls, so they see phone browsing as a voluntary foray into their world. This is reflected in the table near the bottom of the article with the "PDA owner (personal choice)" entry (with Opera glasses on: "PDA? Are anyone still using that?"). The screen reader article is another should-read article, but the link here to the author's web site is more, ahem, accessible for us phone users than the PDF version or the Google de-pdf version.