Haha, I don't know about the unnatural part, but uneducated part probably.

I've heard Japanese people make that mistake a lot of times, too. I've heard my girlfriend called things "hitori, futari" etc before, too. They are definately important, though, as most japanese people don't make those kinds of mistakes.

Besides, by just saying hitotsu (or whichever one you need), hopefully they will say something like, "ya, ichi mai". It's a good way to learn "on the go" as they say (and much like the relationship a mother has with her child when the child is first learning how to speak).

I did, and it makes you sound very childish as well.

Besides, つ only works for numbers 1 through 9.

For the same reason that saying "stuff" and "things" in a job interview in English typically does. Because.