Just like 700mb is very different then 10MB when there was only 56k in the mid 90's.
Lets all agree (for the sake of arguement), that DVD's became the "norm" or mainstream, six years ago. At that time, could you download a DVD from your computer, like you can today? No
So you can take that example, and show Blue-Ray or HD-DVD, being atleast 4 to 5 years away from being the "norm" or mainstream, and then adding a year or so on top of that, to when you can see typical people, downloading hi-def movies
Its only a matter or time, when 20GB is labled as "tiny".
Second, do you really think the infrastructure or technology is in place for 20gig streams to be the norm? Furthermore, its not like the average consumer is using his PC to download DVDs today, even if the bandwith is available.
Lastly, there is one big difference today. 1080p and the fact that the industry is rapidly trying to make large 1080p TVs the norm. Do you really think when large TVs next yer are 1080p that people aren't going to want the content fo their TVs? I actually use a 65"1080p plasma right now and I can assure you that people aren't going to be happy with DVD when they see what HD formats look like on those TVs.
I'm not sure how it is in Europe, but in Japan and the US, the push toward 1080p is already well under way. While the HD formats are slowly picking up pace, players can be bought for under $300 already.