1) they send you / give you access to a link (or list of links) where you can download the book in a "limited fashion" (time, number of downloads ...). This induces almost necessarily the use of a PC to download and manage the ebooks collection.
2) they keep the bought ebooks in a "library" section of their site, where you can download the book "at will". This allows you to remove the ebook from your reader, (archiving), without losing access forever to it. It also allows you to manage your ebooks collection without any other device (PC for example).
The "major resellers" (Amazon, Google, B&N, Smashwords...), and some others (Webscription for example) all work on that second model.
This also allows them to develop a model where you don't even need to download the entire ebook to your device, but use a specific browser to access it on their server as with the "PC version" of the Google EBooks reader. The Book is kept "in the cloud" for you in "eternity", or ... as long as the reseller keeps the ebook at your disposition ...
There have been incidents whrere bought ebooks where removed from the "Library" as well as from the "device" !
So while the Library is that (a Library), we should not consider them "Safe" : the "librarian" can "at will" change the content of that library, either by adding/removing books, but also by "corecting" them the way they choose without our knowing...
If we want to have a more "long-lasting" library, I think we need to maintain our own "library" in addition to the reseller's ones. In our own library, we should have a copy of each and every ebook we have bought, if possible without DRM so that we also will be able to convert them to other future-proof format ... How to set up such a library is left as an exercice to the reader... but I guess you should backup it the same way you do your digital photographs (you DO backup your photos right ?)
This does in NO way mean say that we should NOT use the reseller's library facility (in some way, if our own library goes down, we will be most happy to use theirs as a backup :) ), but we should NOT trust them the same way we would a Safe in a bank.
There is even one comment on mobileread about kindle DRM :
This means that if you want to get rid of the DRM, do it ASAP !Originally Posted by abookreaderUnless something has changed recently that I am not aware of - If the only copy of an eBook you have is one DRM'd for a Kindle with a firmware 2.5 or higher and the books are no longer available to you to re-download from the archives, as of right now you would not be able to strip the DRM.