And all this extra processing is done whether the protocol is AFP, SMB/CIFS, or NFS.
If you are using Windows as a server, and are using Services For Macintosh in order to use AFP, then you are stupid. SFM basically assumes Macs are still running the older non-OS X version of the Mac OS. It doesn't use TCP/IP, it uses AppleTalk which is slow and chatty. Many off-the-shelf NAS devices run a version of Windows Embedded, which means if you use AFP on that NAS you are accessing that NAS via SFM, yuck.
Any network admin that has had any Mac experience at all knows not to use SFM and to use ExtremeZ if the server runs Windows, or something like it. Better yet, use a real server OS and use Netatalk, Helios, or Xinet KA-Share.
Chasd