[ilikeATMs]

Depends on design and cost. Your thinking of a vault. Vaults have a solid door (as described above) and essentially its layers of security. The other 5 sides sometimes are the weakest point, but will still take significant amounts of time to penetrate on any properly designed vault.

No point in putting an extremely expensive vault door in a room that's got just concrete and re-bar.

The other thing is to make it harder to access those other walls as opposed to the front where you can walk up to it.