The 1GB is a cache file it uses on the HDD during gameplay it fills up to help with textures streaming and such I believe. The content of this cache file will be dependant on the levels you're playing too so it's not like it could be a permenant installation of 1GB to help.

Finally the reason Uncharted 2 looks so amazing is the number of tricks implemented in the engine to produce what you see. A big part of this is the clever cache system used to read data from the Bluray onto the HDD in advance so it avoids texture pop in issues that the first would very occasionally suffer. If you made an optional full install then the game engine would have to be altered fundamentally to allow this facility as like Halo 3 on the 360 caching to the same device causes serious performance problems. I doubt it would be worth the weeks of effort making changes and testing just to avoid the 30 second maximum load time when you first start the game up imo.

There's no install.