Under normal circumstances without boot camp or any 3rd party software installed, when you are running Mac OS X, you can attach a NTFS (Windows) drive and read from that drive. What you cannot do, is to write to it. When you connect across a network to a PC, though it takes a good deal of time with Snow Leopard to connect (much longer than 10.5.8), you can read AND write. Why is that? Is it connecting via FTP or something?
When you mount a local disk, OS X is speaking NTFS to the disk using an NTFS driver. The OS X driver only supports reading NTFS. Look for NTFS-3G for Mac if you really need read/write to a local disk.
When attaching over the network, OS X is using the CIFS/SMB protocol which is a network protocol for access disks (and some other resources) just like AFP or NFS. The fact that the actual disk format is NTFS is irrelevant in this case. It is the job of the SMB server to handle accessing the actual disk file system. Windows, obviously, has an SMB server built in. Pretty much everyone else (at least any UNIX-like OS) uses Samba for SMB. This includes Mac OS X, Linux, FreeBSD, OpenBSD, NetBSD, Solaris, etc, etc ,etc. I have Samba running on FreeBSD and Linux servers with the underlying disks formatted with UFS2 and ext3 respectively. My Mac has no need to know those protocols.
As you indicated, this is similar to FTP or HTTP. The server handles the access to the actual disk and communicates with the client over a specific protocol.