For free games we've been using a slower server that's an order of magnitude cheaper to deliver files from. Our bandwidth bill would be well over 10k dollars a month for free games if we didn't do this. We're aware that there are speed and reliability issues with it, especially in non US regions. If you've paid for a game, the files you download will always serve directly from our storage provider (or faster CDN) to ensure the best performance.
For the past week we've been testing out a new CDN that, although a few times more expensive, is significantly faster in most regions. We think the cost to speed trade-off is worth it. It's currently active on free downloads now, so go test it out and report back if you notice any issues. If we don't end up sticking with them, we'll continue to look for a solution to make downloading games as fast as possible (without causing us to go bankrupt).
Regarding providing a torrent tracker, it's something I've though about but haven't looked into the logistics of yet. It could be interesting, but I feel like only a small subset of users would use due to the additional complexity. It could potentially be a good candidate to use in our app though. I know many patchers for games utilize torrents.