The SF publisher Baen Books sent out an email yesterday to its customers with the news that it will shortly have to stop delivering Kindle ebooks via email:
The rest of the email included instructions on how users can email the ebooks on their own.
Baen will of course continue to sell Kindle ebooks DRM-free, it's just that for some inexplicable reason they are no longer allowed to email said ebook to your Kindle account. Readers can still do it themselves, however.
As with any of Amazon's decisions, i would not try to read too much into this. I know that one site is saying that Amazon has changed its rules recently, but I doubt that has anything to do with it.
A member of Baen's Bar found the rule in question, and it turns out that Amazon has always had the rule that this service cannot be used for commercial purposes. The rule exists, yes, but Amazon turns a blind eye to violations.
I can't tell you why or how Baen Books ran afoul of Amazon, but I wouldn't read anything into it other than the obvious conclusion: that Jeff Bezos bites the heads off of kittens.
Seriously, folks, I doubt this change will matter much. I suspect that any reader who is savvy enough to shop at Baen Books is also knowledgeable enough to either sideload an ebook over a USB cable or simply email the ebooks on their own.