Projectiles for bombs, missles, and artillery are divided into many different types according to use.
If you want to take out a building, bridge, radar site, etc, you would use a high explosive projectile designed to inflict maximum physical damage.
If the job calls for taking out troop posistions, projectiles packed with thousands of 1/2" dia. steel shot and equipped with a altimeter switch,(Causes it to explode 20 feet of the ground) would be a good choice.
When trying to attack a fortified posistion deep in a cave, conventional high explosive bombs are really of no use. The Thermobaric bomb probably is somekind of fuel/air, with the intent of removing oxygen(as you stated earlier). It would have to be a laser guided to get it in the small openings of the caves.
However, I still feel nothing short of a cave search, which will be bloody, will bring the Alqueda out.