I suppose that depends on how large the upload bandwidth is. Most people these days (that play online games at least) have broadband, and 400mb doesn't take that long on a 3megabit connection. 18ish minutes. And that's at the low end of most consumers bandwidth. I could download it in 4 minutes, and I live in a small town. Someone living in some place like San Francisco or New York would be able to download it even faster and easier.
Most other places in the world actually have better, faster, cheaper, and more broadband then the United States. That being said, there are still some people out there that do use dial up. I know someone that plays EVE Online using dial up. For people like that, 100MB or 420MB doesn't change a whole lot, it's going to take a huge amount of time either way.
On the other hand though..... If the upload bandwidth of where you are downloading it from is rather low, then it could take quite a while, and that would be a problem. If people really think it's a problem, it might be possible to do something similar to how WoW distributes patches, via direct download with the speed boosted by bitTorrent. They have the whole thing integrated into the game, using the same port as the game and so forth. I know this from the one time I tried the trial, as I had to patch before I could find myself bored and quitting....
