I haven’t been checking each incremental release so it’s possible this landed earlier, but the current version of Apple Pages has improved the semantics of their EPUB export.
The original template now produces <p> elements instead of <div>s, an important update:
<h1 class="s7">Introduction to ePub</h1> <p class="s6">This document will show you how to use paragraph styles to create a publication that looks great and is easy to navigate in ePub readers like iBooks... </p>
Presumably this affects the degree to which Pages-outputted styles are visible in iBooks (as user preferences may override), but it’s great to see more semantically-correct output. This corrects my earlier reservation about using Pages for EPUB creation.