You'll care when the majority of developers will jump to Android because it has more users. Why do you think most people still use Windows? Because it has more software. Once you get behind, it's tough to keep up. Look at Windows Phone 7. They have to pull really hard to get some developers to build apps for them.
I have to say I'm impressed how Google managed to get this off the ground so fast. Microsoft is still struggling, and they have a pool of traditional .Net developers behind them to potentially build apps for their mobile platform.
As an iOS developer, with both a Java and .Net background, I can say that right now, all the money to be made is primarily in the iOS camp. Android users DO NOT BUY apps. That is a generalization, but it is a TRUE generalization. They do not buy apps like iPhone users. There are many reasons for that. One is that many Android users got free or really cheap phones, and don't tend to come from higher income backgrounds. They are less likely to spend money than iPhone users. Moreover, the infrastructure for buying apps is not setup as well as iPhone. All iPhone users can buy apps the second they are setup, that is not true for Android users.
In terms of monetizing free Android apps...they do not pay well when it comes to Ad revenue. For a client's app I released on an iPhone, using iAds, I needed 10,000 daily users at about 1 minute of use time per user per day to make about $5K/month in Ad revenue. In order to get that kind of revenue on a free Android app, I would need approximately 200,000 daily users. That is a huge discrepancy between ecosystems,...it is not easy to get 10,000 daily users, much less 200,000,...meaning developers are going to stick with iOS as long as it pays better.
So for the time being, I don't concern myself with Android as a developer. Now if google finds a way to make Android phones just as profitable as iPhones, or develops an ecosystem much like Apple's that drives app purchases and app revenue to something resembling, or outpacing Apple, then I would be REALLY worried as an iPhone developer and user. I just don't see it happening as Google is more concerned with it's own Ad business, and how to make Google more money, rather than spending more time and effort on how to best make developers money. Apple has struck a great balance that allows them to keep developers happy while continuing to reap the rewards in terms of company profits.