We definitely want to open our releases up to as many people as we can, but for our first game we are specifically targeting the iPad. The main reason we are doing this is that we conceived the game from the beginning as needing a large-screen multitouch device. Also, the barrier to entry at the App Store is very low, there's a lot of people willing to take a $5 chance on a strange new game there, and targeting one device means concentrating all our energy on one codebase, and only having one build for QA.
However- our subsequent game plans definitely include the iPhone, and we would love to one day do some releases on desktops. Our success with this first project will decide how far we can go!