Two things are possible;
1. They restricted the destruction in Beta (Or didn't finish it at the time) so the tower would be destroyed 'realistically' in the retailed version.
2. The tower is meant to be non-destructable, like buildings in Bc2 Vietnam.
Seeing as they said there was supposed to be full destruction of nearly everything, I'm hoping the tower can collapse, possibly being indestructible but the wires can be destroyed for it to become unbalanced. Just imagine it falling into the middle of the map :S
They decided a long time ago to remove full destruction as they didn't want every map to be full of flattened buildings.