1. The ISBN is used by libraries for cataloging and purchasing books—including ebooks.
Libraries are irrelevant to "self-publishing." They're not interested in our books and the way you make money is not chasing markets that aren't open to you, but exploiting those that are.
If you're popular enough that you're likely to get into a library, you probably have an email box full of offers from agents and publishers anyway. And Sara Fawkes or Hugh Howey and the dreams of a lot of people aside, that's really not likely--most of us make our money on lower volume and high royalty.
When my KDP shows thousands of sales a month, then I'll be perfectly glad to buy an ISBN
because it will at that point become financially useful. Until then, it's just pointless. It's a vanity thing. And as a "self-publisher," you can buy one and change your books to it whenever you'd like. It's not something you have to do when you launch one. Just like at launch you'd be very unlikely to do a physical print or audio book, but when you have a hit, it's something you look into.
3. I suspect that you're not aware of just how much information the ISBN encodes.
I'm perfectly aware of it. It's just not particularly relevant. It serves no purpose for 99.9% of "self published" writers. The vast vast majority of sales are ebook format. Author -> storefront -> consumer. No ISBN necessary. No purpose served by having one.
According to Apple, you need an ISBN to sell books
Last I heard, they'd changed their policy. It was one of the biggest things driving people to go through them to Smash/lulu. My understanding is that starting last month, Apple, like ARE, now assign a faux ISBN. (ie, something with the same number of digits, so it fits in their database field, but which can't possibly match a valid one.)
Right now the biggest issue for most people going direct with itunes is the linkage of their listing of publisher to the tax ID used on the account (ie, your real name). The Mac thing is a PITA, but you can rent time on a virtual Mac for a minimal price or buy a cheap used Mac on ebay. From memory, you need to have OS-X 10.6 or better. With the removal of the ISBN requirement a lot of people are looking into it. However, for now, the result is most "self publishers" still go through Smash or Lulu.
The far bigger issue with itunes (and kobo) has to do with searchability, not by ISBN, but by topic, keywords, etc. That's one of the huge strengths of the Amazon storefront: it reliably connects readers with what they want to read. That benefits all authors from the Big 5 to the "self publisher" like me who sells a few hundred units a month.
Going back to the original topic of mainstream publishers opening vanity press imprints, one of the big things you'll find on Archway is babble about how they give you an ISBN to get into a physical bookstore. It's one of the big "tells" that they're a vanity press and selling dreams rather than reality.
ISBNs are as important to "self publishing" as a travel agent is to booking a flight between NY and Chicago.