Android - at least all the code you get from Google - is under the Apache 2.0 License. That makes Android a fully open-source project, since the Apache License is an OSI-approved license (and quite a permissive one at that). So people can't (or shouldn't) complain about Android not being open-source; they should complain instead about carriers making proprietary extensions.
Quick note: CyanogenMod
- an open-source build of Android - comes bundled with its own open-source marketplace application.