For some of the more notable bloggers, because everyone knows they're on Team Apple. They aren't just people who have a lot of Apple products, they're people who have significantly bought into Apple's worldview and culture. Since tech punditry as a whole is very tribal, trashing the other teams regularly is par for the course, but trashing your own team is seen as a betrayal, an extraordinary event, a reaction to the company's own betrayal of the pundit's heightened trust. The latter is newsworthy, the former is not.
(While this mentality is strong in Apple-land, it certainly has its place among Google partisans as well, among others...)
Reminds me of this[1] LessWrong post. It's not unique to tech, it's (unfortunately) part of our tribalistic instinct:
> Arguments are soldiers. Once you know which side you're on, you must support all arguments of that side, and attack all arguments that appear to favor the enemy side; otherwise it's like stabbing your soldiers in the back—providing aid and comfort to the enemy.
I think it's telling that the two things John Gruber blogs about are tech - and sports, where fans are expected to pick a team and be loyal to it. At least in the latter arena, most people treat the tribalism as just for fun!
Which is why I read Daring Fireball. I do like Apple in general, but I also just find it fun to be on a team, and try not to take it too seriously.
(While this mentality is strong in Apple-land, it certainly has its place among Google partisans as well, among others...)