I'm thinkin' their bunkers were built before our bunker busters were created...
I've heard that they built theirs much deeper under ground than Saddam did. They learned from his mistakes. I'm not sure our bunker busters would do the trick.
Check out these articles about Barnes Wallis' earthquake bombs of WWII.
http://www.computing.dundee.ac.uk/staff/irmurray/bigbounc.asp
"...Tallboy's sleek shape enabled it to gain as much speed as possible during its fall, giving maximum penetration into the ground which was essential to maximise the earthquake effect. This speed also gave rise to a couple of problems with the design. Firstly, the ground impact at high speed meant that the casing had to be very strong to prevent it bursting open, and special metals were developed for this purpose; the weight of the case was thus a high proportion of the weight of the bomb so, despite its size, it was classed as a "medium capacity" weapon! Secondly, during trials, it was found to be inaccurate, and this was attributed to the bomb "toppling" off course as it passed through the sound barrier. Wallis solved this problem rather neatly by offsetting the bomb's tailfins; this made the bomb spin as it fell, and the gyroscopic effect prevented the toppling and thus maintained the accuracy...
http://en.wikipedia.org/wiki/Bunker_buster
In World War II the British designer Barnes Wallis of Bouncing bomb fame, designed two bombs that would nowadays be called bunker busters: the five ton Tallboy and the ten ton Grand Slam "Earthquake" bombs. The designs were very aerodynamic with a tail which caused them to spin. This allowed them to break the sound barrier as they fell from a height of 22,000 feet (6,700 m). They had a much stronger casings, made of high grade steels, than the typical World War II bomb so that they would survive the impact of hitting a hardened surface or penetrate deep into the ground.
Though these bombs might be thought of as 'bunker busters' today, in fact the original 'earthquake' theory was more complex and subtle than simply penetrating a hardened surface. The Earthquake bombs were designed not to strike a target directly, but to impact beside it, penetrate under it, and create a 'camoflet' or large buried cavern at the same time as delivering a shock wave through the target's foundations. The target then collapses into the hole, no matter how hardened it may be. The bombs had strong casings because they needed to travel through rock rather than re-inforced concrete, though of course they could perform equally well against hardened surfaces. In an attack on the U-Boat pens at Farge two Grand Slams went through the 23ft re-inforced concrete hardening - equalling or exceeding the best current penetration specifications.