Here's a good explination of what happens during the "ring break-in" process
RING BREAK-IN
This overview may explain why some lubricants (such as MMO) help with break-in. As a number of folks suggested I also used MMO on my latest build and my engine seems to have broken in fine. But I also follow the break-in process of varied RPM's, placing a load on the rings etc from the initial start-up.
good luck,
Mike