Moosp,
The damage from a SMALL device (the type likely to get on an aircraft) in negligable of the aircraft is unpressurized. If it is pressurized however the combination of blast and pressurization serves to push the skin away from the stringers and whatnot and destroys the "Ripstop" or failsafe design of a modern pressurized cabin. So the force of the air going out the hole continues the work with no ripstop to stop it...
Surely you have seen the videos of explove demostrations in pressureized and unpressurized cabins and consequently what goes into determining the "Least risk" bomb location on an aircaft (Usually infront of an aft door precisely centered both vertically and horizontally so you get the rip stop of the door frame...
BTW, on that subject on flight 63 (the shoe bomber) before many of the current procedures were in effect, when they took the shoes from Reid, initially they took them to the cockpit, They quickly figured out that wasn't so smart and moved it to the least risk bomb location, but we get a good chuckle about that right now...
Cheers
Wino