MTV have found out that some Blu-ray games require installs to the hard drive because Blu-ray drives can only read at one speed. "When this is combined with the extremely large size of Blu-ray discs, and simply dumping existing DVD data onto a Blu-ray disc will inevitably result in longer load times."
The issue arises from differences in the reading techniques of DVD and Blu-ray. By nature, the outer and inner parts of a disc move at different speeds while a disc is spinning, regardless of format (CD, DVD, Blu-ray, HD-DVD, etc.). While DVD drives can read data at those differing speeds, Blu-ray reads at one speed. Combine that with the extremely large size of Blu-ray discs, and simply dumping existing DVD data onto a Blu-ray disc will inevitably result in longer load times.News Source: multiplayerblog.mtv.com
Installations are a way around this issue.
When a publisher asks you to install a game on PS3, it’s because they’re moving some of the disc data to an area of your console that has much faster read access: the hard drive. You get vastly reduced loading times, but have to sit through an installation.
I recently read an interview with one developer who stated that much of the space on PS3 discs is taken up by duplicate assets, such as textures and models reused in different levels, can be more quickly read from the disc. I believe Resistance is one example of this. Please check out my new blog!