The reviews for the B&W ASW610 have been good, in its price range this sub rates better than many of its competitors. Check out the What Hi-Fi review, for example.
To claim the PB10-NSD is better without listening to both and basing conclusions on amplifier power and frequency range alone is a bit disingenuous, the B&W's amp was designed by Rotel.
The review mentioned above states:
"However, most of its rivals can go loud and deep: the ASW610’s edge lies [in] its lethally effective blend of power and poise, muscle and musicality."