Many people subscribe to newsletters for exactly the same reason other people use RSS.
I also did it the other way around, and I dearly miss it on 10.8: I subscribed to RSS for stuff that other people use email notifications for. Mostly blog post comments and AppWorld reviews, both of which are often support requests in disguise. Adding the StackOverflow search query for a library I wrote was also awesome. Extremely low traffic & always better to read within a day.
No doubt. But I feel that I'm in a different mindset when I'm looking to read and looking to deal with email. It just reminds me of where iTunes has taken us, from being a music player to become a media and DRM management system. I was happy that didn't try and shove the Mac App Store in there as well.