I disagree. It's not the entire game that it's cached to the HDD.
Is not clear thought, whether that part of the game install is optional or mandatory.
I think it is the whole game that gets installed the first time. The question would be if after you get to certain places in the game and, save there, then continue playing another session in a different time, would it require you to cache all the game again or just what is needed from the part u got to the last time?
Less blu-ray drive use = better. I don't want another PS3 situation where it'll break in a few years.
I understand the concern but, didn't we have consoles (up until now) that made a more intensive use of disc media as the games were actually being always streamed from it? If anything I foresee that this time around the use you will get from the drive will be, if anything, less than previous generations.
Edit: Sorry English is not my first language I do many mistakes with it, that's why I edit a lot (lol).