I buy from Amazon and Kobo because so I am sure I can remove DRM. If the book has no DRM I can buy elsewhere.
But to answer to the OP question: I can only talk about Kindle and Kobo, I don't own any other device:
Kobo will let you read book synopsis/info (like a back cover) without open the book and moreover has a good integration with calibre.
Kindle will show synopsis when You open it and push "information" if the book is bought from Amazon; if the book is not bought from Amazon Your Kindle will connect to Kindle store to show synopsis inviting You to buy the book (I think it is a little strange: I own the book

) I don't know what happens if there isn't that book in Kindle store.