Best practices on IP addresses on a PIX

I have a client that has a 2 PIX boxes. One uses one IP address and serves multiple sites, all on port 80, the sites however are primarily for internal use. This does save on IP addresses.

He has another PIX for his public traffic in this case each site has a separate public IP address. However, a former consultant has placed each site on a different port, on the private side, and the NAT does the translation. I am told this was done for security to prevent “spidering”. It strikes me a unnecessary. Any opitions out there?