In the interest of data-gathering, here's some comments from Naughty Dog on use of HD and BluRay in Uncharted.
source: http://palgn.com.au/article.php?id=9225&rss=1&title=Naughty+Dog+Interview+Part+OnePrimarily the whole experience is enabled by the use of the hard drive. If we did not have the hard drive then we could not present the game in the seamless load free way that we are. After you start until you turn the console off and go eat your lunch and come back there is not going to be another load time and you can play the game from start to finish. That was really key to us something that we established with Jak and Daxter and it keeps you immersed in the experience. As soon as you hit those load screens, as soon as you have to take that break, you may put the controller down, you may do something else we really just want to engross you in this experience. So, the hard drive really helped with that. The other thing that we've got going for us is the Blu Ray. We filled that thing up to 24 plus gigs, it was right at the end where we were literally running out of place where we were having to start pulling some stuff out, we ended up fortunately finding this unused cache of audio lines we were able to pull out to save some space so we could get everything in that we wanted to get in. I'm not going to stand here and say it would have been impossible to do on DVD but it would have been a different game, it really would have. It could have looked worse, we would have had to make concessions in terms of our compression. We would have had to spend a lot more developer resources focusing on how to get it on the disk when we could have been creating the game, making it more fun, making it more beautiful. So I'm really happy just to have that. We're still on single layer and this is our first game out of the gates. So I highly suspect that on our future games we'll even go to a double layer and we're going to even start putting more than 24-25 gigs into a single game.