Well, with a Nook you can get epubs as well, so those would be cheaper. It just seems very roundabout. Kindle prices do seem to be among the cheapest you can get for a lot of e-books. Though it's a walled garden (is that the right term?) for e-books, they do a lot of useful things for the customers. You don't have to worry over things too much -- it's all taken care of. I'm used to getting books online and side-loading them, so it doesn't strike me as a problem, but I can see why people would be happy to just have the book appear on their devices.
I now have free e-reading apps on my computer for Sony (the Reader Library software sucks), Kobo (mixed feelings about the shopping experience and software, but leaning towards "meh"), Nook (not thrilled) and Kindle (seems the best by far). I'm sure I'll do much more comparing and contrasting over the next few weeks. The Sonys have good hardware, but I can see now why reviewers say the software drags them down. The epubs are pretty readable in the Reader Library if you can get them in there.