I'm not sure i understand the "tremendous difference". They are both advertising, the fact that one is advertising a free product in order to then sell access to you to other advertisers seems to me like a distinction without a difference. They are advertising in order to get you to change your behavior whether that is making a post on Facebook that you may not otherwise have made, or buy a different detergent.
Amazon does exactly the same thing. They sell eReaders at close to, if not below, cost and in the past have sold e-books at below their wholesale cost. They aren't doing that out of the goodness of their hearts, they are doing it to drive you "the merchandise" to their site to sell you more stuff.