Yep, even if they have to buy a Mac ($600 for a Mac Mini), that's still cheap. I'm glad my parents spent money on my "software habit," which has given me a lifelong valuable skill. I'd do the same for my kids in an instant.
No; he's met with a $100 barrier if he wants to supply his software to others via Apple's App Store. Creating and developing for OS X and for iPhone OS on iPod/iTouch/iPad is entirely free. The XCode suite and the SDKs cost nothing to download.
I was merely addressing an inaccuracy in your post. And sure it does: there are tons of scenarios where the Simulator doesn't work like the real hardware or doesn't work at all: location-based apps, many audio and graphics scenarios, Youtube video playback, etc.
The (yearly) $100 fee might not be negligible compared to the price of the device (it's still 50% of the price of the cheapest iPod Touch), but if your child already has (access to) a Mac and iPod Touch or iPhone, I don't think it will be that much of a problem.