Emphasis or Italic?

[Anton J Aylward]

What's the difference between:

  <em>emphasis</em>   and <i>italicized</i>
and
  <strong>strong</strong>  and <b>bold</b>

It seems to subtle for my browsers.
The only "difference" I've been able to find is that according to the
O'Reilly book <strong> and <emphasis> are semantic tags, while <b> and <i>
are physical, but, most browsers render them the same way (unless you've
played subtle games with CSS).

_Are_ there any browsers that render them differently?

/anton