One note: the $3 I noted in the article actually isn't CPM, it's Cost-Per-Reach, or Cost Per Unique Impression. This is an important distinction because most digital/display advertising functions on a CPM basis, where one person might see an ad multiple times. On Facebook, when a Page promotes a post, that post is only displayed to that user once.
Brands have a tendency to abuse the trust of someone opting-in, whether that's on Twitter, Facebook, Email, etc. When this happens, most people aren't aware enough to understand the cause and effect - instead of blaming the brand for being spammy, they get frustrated with Facebook.
The News Feed Algorithm and Sponsored Stories are Facebook's way of ensuring a better user experience. By pushing brands to pay a small price for distribution, Facebook gets brands to think about what they're publishing and to take advantage of the targeting options that Facebook makes available, so that their content reaches the right people.