Uhh, you can't return your purchases on WiiWare or Steam. They are both digital downloads.There is a magic price point. In consumer electronics it is $200. Over $200 your sales are limited, under $200 the market explodes.
I think on iOS it is $5. Especially since you can't return it or resell it if you don't like it. With a Wii or XBox disk - I can trade it in or sell it if I don't like it. With downloadable content I can't. So since there is no physical media and associated cost - they can make it cheaper, and since there is less risk to me I might buy it for $5 or less...
Just my opinion though.
If a game company wants, sell a basic version for $5 with in-app upgrades for a couple bucks each...