Well, from the DBAN documentation, it says it preserves the Host Protected Area (HPA), if any. Which means it is just overwriting mapped sectors the same as the tool Doug paid for.

When the drive itself does the erasure, it normally erases all logical sectors, including the HPA. Especially if the drive supports the even better SECURITY ERASE ENHANCED command -- which is supposed to also erase the sectors reserved for defect management. I suspect the thoroughness of this will be manufacturer dependent, and they ain't talking.

EDIT: I guess this HPA thing, which is designed for MS-Windows machines, is the likely reason that real erase programs for MS-Windows are rare. I gather that name brand computers rarely include MS-Win re-installation discs, prefering instead to use a hidden "restore" partition on the main drive.. hidden as in, HPA.