A few of these strike me as being a bit off base.

Take #3: are you actually losing your ebooks or are you simply unable to add them to new devices? Even then, Amazon allows you to deregister devices that you no longer use. Granted, I have had this problem with books that use Adobe's DRM. Moral of the story, ensure that a company's DRM scheme reflects your planned usage.

Take #4: Adobe's DRM scheme allows for books from multiple vendors. There are two cases for Amazon: you either keep your Amazon device and read DRMed books from other vendors on other devices, or you use a device that supports the reader software from multiple vendors (e.g. Android, iOS, OS X or Windows). You don't actually lose your books because you bought somewhere else.

Take #5: This may be true of some ebook vendors that use their own software. As far as I can tell it is not true of Amazon, Kobo, or vendors that use Adobe's DRM. All of these vendors download the book to the device, and it does not require online access thereafter.

#1 and #2 I can't speak for.

I do remove DRM so that I can maintain my own backup of ebooks that I have purchased. But that is my choice and it does not mean that people lose access to their books when the above happen.