I don't think there's a requirement for a pax to be seated in the emergency exit row, but you will be guaranteed at least one pax because of the legroom. Pax at overwing exits that are not manned (i.e. the plug type like on the 738) tend to get, from some airlines anyway, a special briefing to see whether they understand how to operate the exit when requested, and whether they are willing to operate it. If they are not, they are reseated where possible, or pax are asked to swap seats.
There's a nice discussion in the Cabin Crew forum on this:
http://www.pprune.org/cabin-crew/349...tructions.html
:-)
S.