The PS3 drive is faster on average compared to the 360 drive, some multi-platform games were optimised first and foremost for DVD.
I have provided some info and perspectives here:
http://www.vgchartz.com/forum/post.php?id=2052847
Agreed, to understand Blu-Ray you should look at the best results and not the worst results.
Looking at the best results so far, games which required no mandatory installs such as Motorstorm: Pacific Rift, Killzone 2 and Uncharted: Drake's Fortune should provide much insight. Interestingly they are also some of the technically most impressive PS3 games around. It seems games like Heavy Rain and Uncharted 2 may further optimise this trend.
When looking at the worst results, you are mostly judging issues originating from former usage of more legacy technology. Blu-Ray being relatively new, requires different approaches to take the best advantage of. Like a single or double, etc threaded gaming engine cannot be expected the get the most out of the Cell processor.
Not counting the mostly OS dedicated hardware threads, PS3 gaming engines should at least be spread over 7 threads and this is only the first step on the long road for achieving optimal performance from the Cell eventually.
However IMO the PS3 Blu-Ray drive load speed is not remarkably fast for the provided storage space (but sufficient still, all the data on a 25 GB disc can be streamed in less than a hour), as for example, however with regard to average seektimes and loadtimes faster than the 360's DVD drive.
The default harddrive in the PS3 is a lot faster and should be taken advantage of in terms of Blu-Ray streaming (/data caching) and can be taken advantage of in terms of pre-installed data as well. This would IMO make sense for often used files.
So, IMO mandatory harddrive installs can be a pro as you can achieve better results. However regarding many 3rd party games it's just used as a quick and dirty workaround to make up for the technology differences between DVD and Blu-Ray disc.
