I enjoy their wonkish methods,
and agree that the Steelers and Ratties have the top 2 defenses in the league.
When it comes to their overall rankings, however, they simply add up Offensive DVOA, Defensive DVOA, and Special Teams DVOA. IMO, defense deserves more weighting, if for no other reason than the anecdotal "defense wins championships" and the fact that good defenses consistently shut down offenses no matter how potent.
That would bode well for a Steelers-Ravens AFCC scrum and a Steelers SB, no matter how tepid our offense.