Its easy to get caught up in stuff like that on GAF, but do you think the average Xbone or PS4 owner can tell you what framerate they prefer, or what resolution things are running in?
Those who can't get over performance issues, or even those who can't stand the kind of performance most people are fine with (locked 30fps etc) are not being unreasonable, they just have really high standards with regards to performance, but they are in the minority of all gamers overall
Even Unity, which was buggy and ran at an awful frame rate, for a lot of people they found it fine, I have a friend who played it on PS4 at launch and I mentioned the performance issues and he just shrugged and said it looked amazing
Bloodborne doesn't perform perfectly, but compared to Driveclub, MCC or Unity at launch its rock solid
"At launch" is another key thing to remember with reviews. Game reviewers are aware games get patched, they could moan about performance issues for 400 of a 700 word review, and then that review is completely invalidated when the 2nd patch comes out
That review in most cases won't be changed, which then becomes misleading to anyone who might be looking into the game 6 months or more later, I mean, we seen loads of "Is X fixed now?" threads on GAF as it is
Finally, if you send review copies out and someone always spends half the review talking about performance issues they are working on fixing with patches, and that therefore is damaging the hallowed meta score, then maybe they will find themselves not getting review copies in the future