Absolutely!
The Kindle is a wonderful device that is already very good and doesn't improve enough to justify upgrading all the time like Apple devices. And it's very cheap, which makes selling old ones not very appealing.
I own a Kindle 3 (with a keyboard) and couldn't live without it. Even if I eventually buy a newer one I will keep that one to leave at home for example, or give to my kids. But sell it? Never.
This post is quite disappointing, as are most from Priceonomics. They are apparently trying to mimic the blogging strategy of OKCupid, but they're doing it very poorly.