1) Content on post-PC devices is mediated through a central authority. You argue this is bad because presumably you cannot read whatever you want, but only what the central authority allows through. But reading whatever content you want is not enough, you also would have expected that any content you find out there that is optimized for a desktop browser be re-optimized by the tablet device for reading on it.
Response: A valid criticism of the Kindle, though in practice it seems that you are asking for an extension of what is already offered, implying a superset, not a sibling set of functionality. For example, the Kindle has always offered a browser but the technology didn't seem good enough to render a website quickly. Considering that Amazon had its pick of web-to-e-ink and books-to-e-ink, I can't immediately fault them for what they chose to throw their weight behind first--purely from the standpoint of practicality.
You criticized the iPad in your original post, but I don't see any of the iPad's existing functionality being at odds with choice of content provider or lack of optimization for reading web content (see Instapaper, Flipboard, built-in Readablility in iOS 5).
2) Your ability to "produce content" on these tablet devices is hindered.
Response: I addressed this point in my original post. This by and large is a result of the technology available for a holdable computer, not a nefarious choice on the part of the manufacturers. I think the ability to write blog posts on a plastic Kindle is asking a lot (would that even be enjoyable?), and that ability exists on an iPad today, in fact, since it was introduced.