[nicw]

"The main reason, I've heard, is that even if the Kindle format and reader app are reasonable (and I can't vouch for them), it's on publishers to put their books in the right format. "

This is akin to terrible apps on any App Store. It's up to the App Store guidelines to raise the standards and only allow certain books of quality.

Here is my experience based on building ebook-related products:

Amazon: Will allow almost any book of any kind, any formatting. Their singles publishing program is a little stricter since you're giving an exclusive to them and they plan to use those for marketing.

Apple: Strictest store in the business. Humans review every submittal and will kick back your book even if they deem the subject 'not wide enough for a large audience'. IF your book is 51% French, 49% english content but submitted in English, it'll get kicked back and so on.

I don't agree with Apples purview that you can only submit books that are for a large audience - who are they to judge that? Therefore people head to the wild world of Amazon and fight it out at the free or 0.99 level.