Most games preload up to a week before release and you can shape the times it will download as well.
Maybe I'm just a bit more skeptical, since I consider myself to be quite hardcore in that regard. I've got a server that runs 24/7 and downloads pretty much around the clock and I myself see bigger downloads as a hassle. Considering my downloads of multiple GBs over PSN are usually down and installed within the hour, I do know other friends that are less internet savy will not be as patient.
While I agree that the majority of gamers have an internet connection available (or in other words, that the gamers that don't have access to internet is quite small on a world-wide scale), I'm not convinced that that majority also has a good enough internet connection to make it hassle free. For some of them, internet connection will improve over the next 3 years, but not to the extend that would enable 10 GB downloads (and I assume high quality production games will be even larger).
In the last 3 years, I've gone from 15Mbps to 25Mbps. Technically, 100Mbps is right around the corner, just not active in my residentual area yet. I'm not the average customer though, as I pay close to the equivilant of $100 USD a month for internet (I'm from Europe). Most gamers I know, surf around with a medium range package deal. For them, internet access has roughly stayed around 5Mbps. At best, I'd expect them to move up to around 15Mbps within the next 3 years without having to pay significantly more for their internet access. Hardly enough to make DD "hassle free".
Then there are more than few that I know that prefer to have a physical copy of whatever they buy. Downloading legal movies is already an option to many, yet in most cases that I know, the physical medium is still way ahead in sales.
Also, if DD becomes true, what about harddrive requirements? Sure, it wouldn't stop hardware makers to go the cheap basic entry of only offering a 250GB harddrive in its console. At 20GB games + data, you'd be lucky to get around 10 games on it at once. What if you want to play something else? Delete one and wait 10 hours (not assuming high end internet subscription) for the game to download? I've got about 20 PS3 games mind you.
What about harddrive crash? Think about the hassle...