Sorry if this has been answered but I'm too dumb to find it.
Why is it that the simple formatting tags <b> <i> <u>, etc. aren't allowed by the EPUB spec?
These these tags would allow the reader to disable the formatting information from the style sheet (CSS file), and thus allow them format the document to their satisfaction, without losing the important context provided by these tags.
Johnny looked at the cloudy sky. <span class="ItalicClassDeclaredInTheCSS">What miserable weather we're having</span>
Johnny looked at the cloudy sky. <i>What Miserable weather we're having</i>
The former would "break" if the CSS file is disabled whereas the latter wouldn't.