You got it all wrong Mike. GDS only downloads Gmail, as you noted, and any gadget data needed if you are using them.
All GDS traffic goes to local host. Look in your browser location bar when you do a GDS search. You will either see
http://localhost or
http://127.0.0.1. This data is network traffic and every time that GDS indexes or searches that data travels over TCP even though it is traffic that is all local to your computer.
Your firewall will show this as TCP traffic and report it, as it should. It is normal. Your data and your searches are all local, but they are happening over the loopback adapter for your computer address.
You can verify that what I am telling you is true and correct by disabling your Internet access and either waiting for GDS to index more or by doing enough searches in GDS to make the TCP ticker in your firewall move up. Internet access or no the GDS TCP traffic ticker will grow with every index session or search that you do.