http://feedback.arma3.com/view.php?id=14849 has been resolved in this release and I agree that to "destroy a large building that is made out of concrete with one demo charge." "should not be possible".
This extra damage is confirmed by Cochambre here:
"BI changed the amount of damage that towers can take. Instead of all towers taking 1 explosive charge to destroy, larger towers now take 3-4 explosive charges and smaller towers take 2-3 charges to knock down." This I also assume is feasible.
However, unless placed directly in contact with an Ammobox (eg. Box_NATO_Ammo_F) it can take up to 4 explosive charges (SatchelCharge_Remote_Mag) to destroy the object.
Now I'm no military expert, just a gamer, but I am going to assume that a box full of ammo is not going to take more than one explosive charge within close proximity to destroy.
There is also a good indication that this would be the case based upon the fact that during the new campaign you place one 'charge' on a downed ghosthawk to finish it off.
My believe is that either the satchel charges are to weak or the ammoboxes are to strong.
An ammo box can be destroyed in 6 x 6.5mm rounds so I'm going with the satchel charge now being to weak.
I would also therefore assume (and mainly because I have no idea of how to test this) that a building nearby (5-10m) is not going to take a lot of damage from this but someone else will be able to answer that.