The camera icon is not just a picture of the physical world object. It is pretty universal symbol for taking pictures. When the same symbol is used in so many places, even people who have never used the physical object resembling the icon, will recognize its meaning.

In my view the reason behind many of these user interface changes is not really improved usability. The simple reason is that no matter how good interface you design, after some years it just starts to feel old and boring. Old and boring is hard to sell. Fresh and exciting is better. Therefore we keep on changing stuff, even though from pure usability perspective it would be better to stick to the old and boring but familiar.

Easy to use systems make happy customers, but they don't necessarily win the customer's heart at that point when the purchase decision is made. Maybe this is one issue for Apple? Maybe the "old Apple" was happy giving out xx% of their sales for a bit of ideological reasons, but the one needs to find growth where it can? One could see this kind of hints in the product lineup. I would say back in the days it was pretty opinionated, now there's 4 different iPad models (and countless variations).