[zelphirkalt]

> Very surprising to me was that there is a semantic difference in <i> and <em> (the same is also the case with <b> and <strong>) apparently, also PDA readers for e.g., blind people are also aware of this semantic difference.

It is in the names:

<em> = emphasized, as in "this part of the text should be emphasized in whatever way the styling dictates

<i> = italic, just a way to style directly

<strong> = strongly emphasized

<b> = bold, just a way to style directly

<i> and <b> do not make a statement about semantics, they are for styling, and probably not much used in modern valid HTML, or at least should not, if you have CSS available. <em> and <strong> make statements about importance of a part of text, in whatever way you want to style that. It just happens, that the default styling for those is italic and bold.