Had some time left on our 737-800 simulator session the other day and tried a few take-offs with clean wing:
Perhaps the 15 years of development between the MD-80 and the 737-NG make a difference?
The 737-800 has about 5% lower wing loading then the MD-82, not considering the winglets, so that may cause a small difference.
However, your text implies the simulated rotation was at a Vr appropriate for the flapless configuration, whereas JK5022 in all probablity rotated at the Vr for the intended, flapped, configuration. Big difference I'd say.