fwiw, I don't have to forward any ports at my router to allow bittorrents to work.
Without ports forwarded people can't connect to your computer... you can initiate a connection to them, but if they are trying to connect to you, you can't/won't answer. In this situation you can download torrents easily because you are reaching out to them, but if you are trying to seed a new torrent from scratch, it won't work, or it will work miserably.
Disclaimer... this was certainly the case a few years ago. It's possible that UPnP and new trackers have changed this, but not that I haven't heard of it.
Things must have changed...
I have 7 active torrents all with over a gig uploaded and one as high as 6 gigs.
I'm using qbittorrent on ubuntun with a netget wr614v9 router.
Try turning your ports off and see if downloads can still occur.
I did a little more reading...
The torrent protocol didn't change, it's just that routers changed to allow you to be sloppy/lazy. You are probably forwarding ports whether you realize it or not because your computer (via the magic of "universal Plug and Play") asked the router to do it on your behalf. You may think "Oh, that's slick", but UPnP is a huge security risk. If your torrent program can ask your router to open a port without you realizing it, than probably a virus can do it too.
Anyway, it may work automagically in your house, but if other folks have UPnP turned off for security reasons, they will have to configure it manually.