phranque - 2:34 pm on Nov 11, 2012 (gmt 0)
mainly/purely a semantic difference
there is a technical difference and if you get it right then google will recognize this and treat it properly.
if you're doing it wrong, then google will sometimes recognize this, especially if you are big enough to matter, and eventually will sort it out, but there will typically be a noticeable lag.
it is true that these types of technical problems are so common that google doesn't penalize sites per se for exhibiting them, but there can be side effects that affect your ranking.