> The 10.0.0.0/8 block provides 16 million addresses
  > and there's also 172.16.0.0/12 and 192.168.0.0/16.
  > There are certainly enough addresses in these ranges
  > that running out is not a concern

With the constraints of subnetting, it is a concern. I know a very large telco that ran out of private IPv4 addresses - and that specific issue was the reason for finally launching a proper IPv6 project.