Inbox-zero isn't so much zealotry as a method of managing to-do lists. In the business use case, there seems to be a tipping point where the alternative is that other people are responsible for things they send you, which you might drop because they get buried into your 10,000 other e-mails and by the time you get to them, you might miss some. If you're in a culture where task assignment can happen through e-mail you're almost forced into some variant of inbox zero -- particularly if people aren't going to be following up to check on your progress on small tasks until they expect them to be done at the next meeting.
Good question, would seem there are enough to warrant the creation of quite a few email products that are supposed to help you get to this "zen" like state.
One of Mailbox App's pitch points is even along these lines: "Inbox zero. Daily.".
I've been using Mailbox for a while and the only thing it's really helping me with is the ability to either archive-or-delete, which none of the other clients can easily do.
My main problem is that with my style of thinking, I'll get an email that will make me think, "Yeah, I want to do something about that... later." But not "later" in terms of a calendar date - "later" in terms of when I am enabled to work on it, as in when a blocking dependency disappears. I can't find an easy way to make those emails disappear until they are triggered by me completing other things I care about.
Sure, but it doesn't scale well when you're looking at reviewing fifty labels every day to decide whether you're enabled for any of them. Cognitive load. Better for them to disappear and then automatically reappear when you've completed the blocking project.