There's still incentives for app developers on other platforms!
I think what people might be forgetting is there are still incentives for developers on the closed platforms. Just because there may be a smaller userbase than iPhone users there's also less app competition.
What is better? A large chunk of a smaller userbase with bigger exposure, or a small chunk of a large userbase will less exposure?
Depends on the users of the phones, income, propensity to spend on apps, price point, and how good your app is against similar offerings etc. So there's more to consider than how many users?
P.s. I too own on iPhone, but I'm more excited about Android and it's possibilities to dev's and consumers alike!