Actually, there's an interview out there (I'll find it) where ND explains that they were well over the capacity of a single bluray layer with this game, but the turn-around of burning test copies for their testers was too long. Combination I assume of having more single layer burners around and single layer burning being faster.
So instead, they decided to work hard to keep the game within the confines of a single layer. That's also why its exactly the size of a single layer bluray disc - they've already been compressing stuff to make it fit.
I don't think ND designed their HD-caching streaming engine (the first version of which they coded for Uncharted 1 a day or so, iirc - there's a GDC presentation called the Tech of Uncharted I think which details this) so that they would then also need to have their data repeated all over the disc. A combination of the HD caching and Uncharted being a mostly linear game so you can access most data nearly sequentially, there should be no need for that whatsoever.
There were some load-times in Uncharted, although they were hidden by movies - but if you tried to skip the movies fast enough, then you'd still see a bit of a load-screen. It will be interesting to see if they managed to get rid of loading altogether this time (reminds me of Jak & Daxter, which was a no-loading time game on the PS2, which by the way didn't have a harddrive available for caching
).
Really look forward to this game, and to see that depth-of-field in action ... and I also got a nice proper surround system this year that sounds like it'll be getting a good exercise.