There are many ways to have a Linux system automatically download things.
Command line tools such as
curl are one method, as are the plethora of bittorrent applications for Linux. You can even do a remote X session and get Iceweasel running if you have to use a browser.
The thing you want to download will need to work with an available Linux tool. There's no easy way to make something that isn't aware of the Pi's existence download something "batch-style" on another machine's behalf.
So if an application requires its own client to download patches, unless you or someone is willing to reverse engineer that client, you don't have a way to tell the Pi to do that for you without the client.
I'm not sure if Steam patches can be downloaded manually or without the client. If they can be, then you can tell the Raspberry Pi to do that.