I think the point is that given a set of skills and resources (i.e. Cocoa & great design skills) it's way more profitable (5x in TapTapTap's case) to direct them towards iPhone development.

There are different opportunities on the two platforms, but the difference in profitability will absolutely draw some people away from Mac development: it's drawing people away from everything — I know at least 5 ex-Java or .Net guys doing iPhone development full time now.

> it wouldn't be long before the majority moved back to the Mac when the iPhone Dream didn't materialise.

It might be less competitive, but it's not like Mac development is a sure bet that you can just fall back on.