Hey Hun, I asked the same question recently. I read an article about the same thing, and Laura is spot on. Formula manufacturers are not allowed to market or advertise or have special offers on newborn formula so they created 'follow on' and 'hungry baby' formulas specifically to get round it.
We're still using newborn formula. In answer to your question re iron in her diet, I guess my answer would be the same as Laura's - as long as she has a reasonably varied diet she'll be fine. And bear in mind that may mean that she only 1 or 2 things for a week, then 2 other things the next week - I guess I'm trying to say that it doesn't mean a balanced diet at every meal. Make sense?