In this thread

http://www.flyertalk.com/forum/conti...er-flight.html

Several people say the international rules for the baggage apply as it's all on one ticket, even with the stopover.

And a first hand experience in this thread when they said it was an international ticket

http://www.flyertalk.com/forum/delta...stop-over.html

and another one on American

http://www.flyertalk.com/forum/ameri...-stopover.html

and one on United

http://www.flyertalk.com/forum/unite...-stopover.html

To sum them all up it appears that international rates for baggage will apply if they are on one ticket. There were many people saying that would not be the case, they did not seem to be actually flying. The people who checked bags were not charged.