Matt Gemmell posted this well-reasoned and well-written piece on what you get with "open" software development with the Android platform and what the real cost is to developers. It addresses the obvious points about piracy and security but it goes far beyond them.
Key in the piece, to my mind, is the idea that having a business and selling things in an app ecosystem doesn't just mean people make money. It means that people will write more and better apps for your platform. It becomes a virtuous cycle. The more and better apps that are on a platform, the more it will attract other good developers, etc.
Yes, the motivation is to make money but the whole result is far greater than the sum of its parts.
It is a great piece and sums up so much of what has been rattling around in my head these last few years.