The enthusiast would likely not have a problem with hard drive space, but it might become cost prohibitive to the masses if they were to buy only D/D Retail Games. Then there is the issued with monthly download allocations from ISPs, with one game, some people will hit their bandwidth caps (20/30GB/mo). Until ISPs get with the times and allow generous or unlimited bandwidth schemes then I think D/D will be seriously limited in how large it can get.
But for me, its comes down to having a hard copy and transferability for trade ins, selling, & borrowing/lending with friends. As well, it means hands off for the seller, they can't revoke your purchase like Kindle's ebook issue a while ago. With digital distribution, I don't think we'll have that choice.
Here's hoping for more physical media in the years to come.
Exactly! It works well enough for DLC, Expansions, & PSN games, but for full games it should never be forced. The option would be nice to have, but people would need some serious hard drive space and internet bandwidth.