You, sir, should read the next paragraph in the Wikipedia article you linked to:
A customer may or may not also be a consumer, but the two notions are distinct, even though the terms are commonly confused. A customer purchases goods;
That would be advertisers paying money to Facebook in exchange for your data so they can target ads at you
That would be you clicking Like on that Miley Cyrus video, generating the data (the product) that the advertisers are willing to pay Facebook for.
An ultimate customer may be a consumer as well, but just as equally may have purchased items for someone else to consume.
That would be the advertisers (the customer) providing the revenue Facebook requires to provide the service to you (the consumer).
I already covered this in my previous comment, but maybe I failed to make myself clear. Yes, Facebook users exchange their data for the use of the service, but their data in and of itself is of minimal value to Facebook. Sure, it may give them opportunities to expand their user-base, for example. Especially if you are willing to allow them to harvest the contacts in your email client.
It is the advertisers who value you data, and are willing to exchange money for it. That provides the revenue Facebook needs to keep operating.
You are providing a resource to Facebook in return for the use of their service, which they then refine and sell to their customers. It's no different than the farmer who grows the potatoes that McDonald's turns in to french fries, except the farmer is probably being paid in cash rather than cat videos.
Is the farmer the customer?
Here's a better analogy, and it even has a car in it:
I'm a high school kid and my dad runs a used car lot. I come in after school and on weekends and wash cars on the lot so they will be more appealing to my dad's customers. He doesn't pay me, because I'm his kid and he's a cheapskate, but in exchange for my efforts he occasionally lets me drive one of the cars from the lot.
So I'm giving something that is of limited value on it's own, but increases my dad's ability to generate revenue for his car lot so it can stay in business, and in return receive the use of some of the company's assets.
Now substitute washing cars with clicking Like buttons, and using cars from the lot with using the site, and you begin to get the picture. The fact that I exchanged a bit of labour for the occasional use of a car from the lot does not make me the customer. I'm more like a supplier, or a sub-trade even.
But I'm sure I'm not changing your mind about anything, if you've even bothered to read this far. If you want to think of yourself as Facebook's customer, go right ahead. But your use of their site on its own generates no revenue, and without revenue a company isn't viable. In my book the actor providing the revenue is the customer. They are the ones my business will cater to.
Having someone wash the cars on my lot is great, and might even help my business, but without cash-paying customers my business will fail.