Perhaps, but you don't turn around and give the shampoo producer intimate details of your life. Instead, you probably forget that you have the sample and end up throwing it out 6 months later.

They're different businesses, I'm not sure that you're comparing apples to apples.

We don't know how many people sign up because someone said it was cool or invited them and then forget that they have a Facebook account.

It serves Facebook to publicize a giant number to make them appear unbeatable, but the numbers that count aren't about number of users - they are about usage.

I think it's a reasonable analogy.