The primary reason for telephone exchanges of the past being built on
ground floors and basements was the weight of the equipment and the
difficulty of moving it. In modern times, the weight of the batteries
still plays a role, but exchanges are being remoted away from the batteries
with increasing regularity.
Mae-East is pretty good example of this still.. those DC batteries didn't
appear to me to be featherweights, up ontop of concrete blocks. I don't recall
seeing DC batteries in mae-west up in the building.. where did they put
them?
The cost of building a datacenter in a multistory building is much much
greater than a one story building, as we have learned. The only benefit we
have seen from the multistories, is the usual coincidence that they are
more likely to be "lit" with glass, than a vacant one story.. unless you are
acquiring an old bell building or something.. owen 
rob