I can set a max uplink speed with my torrent client to prevent this from happening. I know, most end users are idiots...

Torrents would simply supplement the bandwidth provided by GoG. There are people (not I) with extra upload bandwidth they can spare. Let them share if they want. Torrent works really well for people with slow connections that can only download a little bit at a time. They can turn the computer on, download some, then turn it back off. If they are working on their laptop they can easily break it apart as they move from location to location.

Your point at the beginning is valid though. A good download manager that does perform all of the torrent type functions of easy pause/disconnect/restart with high reliability would solve these problems and make this discussion moot. While I've only downloaded one very large game (Witcher 2) from here without issue, it seems that those with less reliable connections don't have that luxury.

Other than Blizzard that was already mentioned, I've also encountered torrent-like behaviour when I downloaded the Windows-7 open Beta 2 years ago (or was it one?) from Microsoft. I say torrent-like because while the client had the torrent-like behaviour of upload/download at the same time, neither the client, nor the .torrent equivalent file were recognized by any other torrent client at that time. I'm not even sure if they used the same hash-protocol to ensure non-corrupted chunks.
So, taking a look at the BitTorrent protocol specifications, I think it would be possible for gog.com to program a torrent-equivalent optional downloader, using most of the strengths of the BitTorrent protocol, while still being different enough from normal torrents to not allow anyone to use it. Add to it that you do not have access to the .torrent file, since that is done server side by enqueing the game to be downloaded (like with the current gog downloader) and it would be a nice option to have (assuming you can also add the extras for download as well).

On the other hand, that is gog's decision.

I thought I read somewere that services like steam for 3 cents USD it is about a gig upload. So probably wouldn't help too much. Though maybe for the witcher 2. the one time I would have loved this is not on gog but steam. LAN party and my friend and he doesn't have the game we want to play so he starts d/ling it. It was like 7-10 gigs and capping out at 400kb/s. Why they won't let me send it when 3 other people connected on gigbit ethernet is just silly. If it was gog i would have had him buy it and i'd just send it to him or pass an external drive.

The better answer might be more legal, gog owning the limited rights of distribution might not include allowing users to distribute copies even over a private network.