For once I agree with Apple's big-brother…ing. iBooks lets you choose a font for the content you're reading, and it'd be an absolute nightmare having content that isn't consistent.
If I'm reading the article correctly, though, iBooks is making content less consistent. If the author puts custom fonts on all their tags, iBooks is going to honor all of them except <p>, <div>, and <span>. So you'll be reading along in Apple's serif typeface, then suddenly there will be a word an <em> tag rendered in sans-serif italics. As the article author said: "Ew."
