1. The Kindle is a GNU/Linux e-book reader -- it runs a Linux kernel + userland atop an ARM chipset. The only thing "proprietary" about the system is the actual GUI tools for browsing/buying/reading books, and the radio firmware (pretty much mandated by the FCC).
2. The Kindle "experience" is very much different from what you get from reading on a laptop, even when suing a very compact model like the Eee. I've been reading book-length text on LCDs for years, but the Kindle is the first device that has allowed me to totally forget that I'm not reading a printed volume. If you haven't used one for at least 15 minutes, you really haven't had a chance to evaluate it fairly.
3. Finally, Amazon has never asserted any right to so much as examine what non-Kindle-store content you have on the device, much less delete it without your permission. Conversion of content from non-Amazon sources has been a feature of the Kindle from day 1, and any documents you acquire from other sources can simply be copied by using the Kindle as a USB mass storage device.
Like any hardware/software bundle manufacturer, Amazon has the option to render a large portion of the installed base of devices less useful via over-the-air provisioning. However, like other companies possessing such power (Microsoft, for the XBox 360; Apple, for the iPhone; not to mention basically every smartphone on every carrier) they have to weigh any potential change against the risk that their customers will go elsewhere.