The Korean embassy page that is linked to from the IETF meetings page
(<http://www.koreaembassy.org/visiting/eng_visas.cfm>) makes it
pretty darn clear that US folks should get a visa. They do have a
link from that page saying how wonderful US-Korea relations are, of
course.
What part are you reading that says this?
"# You may enter Korea without a visa for a stay up to 30 days
or less for tourism, visiting, or transit to another country when
carrying a valid US passport."
Seems to me to pretty clear that a visa is not needed.
-Kevin