NAT reduces the number of discrete IPs needed for an Internet connected site.
It allows the restricted allocation philosophy, it doesn't cause it.
NAT allows us to put a larger number of hosts behind a smaller prefix
than would otherwise have been possible. It doesn't directly cause
the growth in the routing table size, because those routing table
entries would have been equally necessary if those hosts currently
behind NAT were using global address space.
In a sense, NAT may have been responsible for a false sense of
security regarding routing table growth - because much of the growth
in the network was within NATted networks, it wasn't immediately
necessarily for those networks to allocate large amounts of global
address space. But as those NATted networks grew to support more
users, some of those networks' operational requirements would have
naturally increased to the point that they needed more reliable external
connectivity through multhoming, which in turn would require additional
entries in routing tables.
Thus, while NATs may help conserve the global addess pool, they do not
necessarily conserve routing table space to the same degree.
But even as a dedicated NAT-hater I cannot find much fault with NAT for
this reason. (I blame NATs for other things, but not for this)
Keith