I don't think of the iPod as a closed system ... but then, I don't think of the Kindle as a closed system either.
I can put mp3s on my iPod, or I can purchase mp4s directly from Apple. I can put mobi format books on my Kindle, or I can buy azw books directly from Amazon.
If I want to play dodge the copyright, I can take mp4s off of my iPod, burn them to CD, burn them back to mp3 and play them elsewhere on a device of my choosing, and I can take azw files, strip the drm, and read them on any mobi compatible device.
However, just as Apple has not seen the need to license out their hardware, I see no need at all for Amazon to do so with the Kindle. Just as I can use my iPod without ever having purchased a single tune from the iTunes store, I can use my Kindle without ever having gone to Amazon.
I realize people are a bit tired of the Kindle/iPod analogies, but in this case I really do feel that it holds.