It's worth noting that Steam have a backup option - which means that if you know someone or could go somewhere with a good internet connection, you could sign into your Steam account having bought the game, log in somewhere with a good connection, download it and backup to a disc or removable drive; return and have it installed on your PC that way.
If we're lucky, you might also have the pre-load option, which lets you download it in advance of the release date, which will mean even if it takes a long time, you'd still have it on time.
I certainly think a DVD release would be good - but there's a few other options out there for those with slow personal connections.