I'll take a guess and say this is as a result of intell gleaned from the failed attempt to put AQ inside the Green Zone.
That's my guess to. The fact that they are using so much firepower leads me to believe that they have either found a large contingent or they are targeting a huge (read Al Zarqawi) target.
There was the recent spate of deaths that the MSM characterized as sectarian violence..
I believe that was actually insurgents being killed by citizen militias..
In the case of those 4 that were hung, they were identified as having been caught with bomb belts and mortar tubes..
I'm thinking this is the same sort of thing..
Locals are identifying insurgent's strongholds, safehouses, and bomb factories, and passing the info on to "freinds" in the Iraqi military, freindly US soldier contacts, and anyone else they trust..