They both seem, IMO, to want to force you into their store for ebooks (Amazon somewhat moreso than Sony). They both "created" a new format, peculiar to their own reader. Yes they both do alow some other format capability but I have to side with Jon on this. Again IMO the reader should attempt to force the ebooks into some particular format. If all readers were able to read all formats then we could select readers solely on the merits of the reader. As it now stands, anyone purchasing a reader must tak into account the availability of ebooks in a readable or at least a convertable format (for that reader).
It is obvious to me that both Sony and Amazon want to tie you to their reader for exclusivity. This comes at the cost of the authors, publishers, and readers.
This is why I eventually went to the Hanlin V3 family with OpenInkPot firmware.
This contest between Sony & Amazon (other players are mostly on the sidelines) is different from the video tape contest (Betamax vs. VHS). With the video tapes there was a physical (i.e. hardware) difference between the VCR. All of the eink reader hardware are capable (with the right firmware) to read any of the ebook formats.