It's a different market with a different culture. Even at $9.99, Avadon for the iPad is more expensive than pretty much ever other game, except for SE's Final Fantasy series and their shallow Rings of Chaos. The game is certainly worth $9.99 (and $25 for the PC/Mac version), but value alone doesn't determine whether something sells.
iDevices users are used to paying $0.99 to $1.99 for the vast majority of games, so anything that costs more is seen as "wow, that's expensive!". It's peculiar to observe if you game on other platforms, too.
I hadn't bought my iPad2 for gaming, but it somehow became my go-to gaming device after just a few days. (And ironically I barely use it for the purpose I had picked it up for: as a study tool for Go, the board game.)