Android is open-source. What is not open-source is Sense or Blur, or the Gmail or Maps clients. You can't assemble the bundle that is preinstalled on your phone just like you can't download the TiVo software and turn your PC into one, even though the little gizmo runs Linux (as does your Panasonic, LG or Sony TVs, all of which run some flavor of Linux).
Additionally, vanilla Android on a consumer device is fairly rare. Most are molested with Sense or BLUR or whatever tragic "vendor-added experience" Samsung inflicts. So in reality, most consumer Android phones aren't really that open source at all, holistically.