The thing going on here is that the bomber does not expect to use the pressure cooker again. All he needs is a container that will stay intact for a couple of seconds while the black powder combusts far more fully than it would under other conditions.
When the pressue cooker lid fails to seal against the power of the expanding gases inside, it lets loose explosively and the gas rushes out pulling with it the debris used as shrapnel.
Why not an old fashioned pipe bomb
6-8 inch threaded steel
Packed with either style gunpowder
Screw caps
Coated with projectile crap
Presto cooker seems like far less explosive compression than capped pipe....even worse than glued pvc
Lol...I know just who to ask?
For an excellent example, watch Bill Clinton's face and finger as you ask him why he let Bin Laden go 6 times.
One of the other things about the pressure cooker idea...It can be somewhat sealed and scrubbed, or washed in a substance after it is loaded with the contents, to make it smell different than something dogs might miss if that was a security issue...