1) Android does not give you privileged user access (there are ways to break the lock, but it is an 'illegal' procedure)
2) You must have a Google account.
3) You must develop in Java, for their specific virtual machine

I am sure points 2 and 3 will be bypassed by creative individuals, sooner or later, as point 1 has been bypassed. But those limits should never have been there in the first place. If people want to keep their personal data in Google's computers, this is fine for me, but it should not be compulsory. I for one prefer to manage my own mail at home.