Typically ebook readers are larger than PMP's with larger screens. If you're going to read for a few hours, then the screen of a typical PMP becomes pretty eye-straining (due to size, contrast, and brightness).
The Kindle has many flaws, but it does allow you to read a few different non-DRM formats.
Non DRM Mobipocket format is already supported on the Kindle - just drag and drop.
The Kindle DRM wasn't hacked to REMOVE the DRM from Kindle purchases, but added to other books so that they too could be read on the Kindle.
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