The forward sweep allows a component of the centrifugal force to counter the drag, reducing the load on the hinge. I believe the R22 main rotor has and element of this in its design and I know that the Lynx MRH has the 4 blades shifted forward slightly for this reason.
If the MR blades are shifted forward, wouldn't that just be pre-lag? Shifting the whole blade, feathering axis and all forward of the hub centerline is a common tactic to reduce stresses with respect to bending in the lag direction. The S300 main rotor has this feature too.
-- IFMU