I agree it felt a little spammy, but I'm so used to people online selling their mothers to save a few cents (think Groupon). Discounts are pretty much part of the American culture. Not this time, though.
Overall, what everyone is telling you (here and in the comments on your blog post) is that putting links and/or endorsements on a social networking service is much more than just a fee-for-service proposition; there are other intangible qualities that are important, primary among them what your friends on these social networking services think of you. You want to believe that your friends post links to things because they're good, not because they're getting a discount. In fact I'd argue that one of the main reasons people like social media in the first place is that it's a person-to-person interaction that's not commerical in nature.