They do host them on their servers, sort of (if you're asking how ad brokers work that's a bit of a different scope).
Does poo have to be on your desk to smell it?
The post office (website) is telling you (your computer) to go over and pick up a parcel of poo (an ad) that's there for you.
You say no, I don't think I will (adblock/poo block)
Wow that's a pretty damning indictement of the product.
To be able to go from "pirated games tend to sell more" all the way to "pirated games with this added not only negate that effect but go so far as to sell fewer copies" is an impressive feat
So, if I'm understanding your intent correctly/distilling it out a bit: you want a feature that lets you seed a new public torrent from a private torrent (using the same local files) in one click?
I'm not too familiar with the plugin APIs of a lot of torrent clients but this sounds like something a plugin could handle.
I have it in a bottle, works great. I just wish the resolution wasn't so ass