Erk....I hate to disagree with Radek....but I really wouldn't mix CIFS and NFS for end-user file serving....the permissions there can just get really complex and in some cases become a security issue. I like sharing out the same volume via CIFS and NFS as a way to transit batch type files between Windows clients and Linux/Unix boxes (i.e. batch processing that regular users can dump files into a " filequeue").
If you look at the traffic, I'd bet the Mac is doing more to provide a "rich experience" -- stuff like the .DS_Store files (you can turn these off and you should), pulling the file down to generate a live preview (I think you can control this), etc.