That is correct; Amazon content can only be read on a Kindle, or on a PC or an iPhone/iPod Touch, using the Kindle application for those devices.
Pretty much every device on the market EXCEPT Amazon uses the ePub book format; Amazon use their own format (essentially Mobipocket format).
It is possible, with a little effort, to convert Kindle books to other formats, but it's a lot less hassle to just be able to buy a book and read it straight off.
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