Is it? I admit I don't know how the number is chosen, but think about it for a moment. With what I have seen here it is entirely conceivable that each "independent non-denominational" Christian church is teaching its own particular version of Christianity. There are enough variables for this to be so. Imagine you move to a new town and are looking for a good "Bible-based" church. So you start going to Pastor Bob's. This seems good until one Sunday he starts talking about free will.
Well, that's out, so we go to Pastor Rick's. Things are good for a months and then, out of the blue Pastor Rick starts totally screwing up his sermon on Revelation. Darn, gotta find a new church.
Then you go to Pastor Bill's. He seems reasonable, then one day he starts talking about when Jesus became God. He thinks Jesus became God at His Baptism. Well that's just wrong.
Pastor Mike's church is very friendly and we asked a lot of questions before we decided to join. And then last week he revealed that the Holy Spirit told him that Jesus was a second God.
Do you see the pattern? Without a written Catechism and strongly influenced by the pastor's own personal interpretation it is entirely conceivable that no two "independent" churches teach the same thing. And the people in the pews are only there as long as the pastor agrees with them.
SD
I think most independent churches will have a statement of beliefs to which they adhere. You think they are run in chaos (and while some of them may be), you are arguing from your lack of experience. You cannot say that they do not have statements of faith. And I'm sure no one wants to take all the independent churches statements of faith and compare them. But until one does, one cannot make the claim that they are separate denominations.
Plus, if you're arguing that doctrine is all that separates one denomination from another, then you have to remove several denominations from the list as all that they differ on is their church structure, with no discernible differences in doctrine.