I just took a look at the energy & broadband solutions listed for these quakes on the USGS site.

Sumatra:
Me 8.5
Es 1.1*10^17 Nm
http://neic.usgs.gov/neis/eq_depot/2004/eq_041226/neic_slav_e.html

Japan
Me 8.6
Es 1.9*10^17 Nm
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usc0001xgp/neic_c0001xgp_e.php

As you can see, the Japan quake's radiated energy is 73% greater than the 2004 Sumatra quake which is officially a 9.1 moment magnitude.

I suspect that when all is said and done, Japan's quake may come in as 9.1 to 9.3 moment magnitude.

Unless, I could be misunderstanding the relationship between Mm, Me, and Es.

Brian