That's correct. The tablet version is not open-source (they probably embedded some proprietary code in it in order to make the deadline). The 4.0 series is expected to unify the tablet and the phone OSs and be open-source.
I always assumed that if they open sourced 3.X, people would start putting it on phones, which it is not deemed ready for yet. These devices would certainly not get official certification from Google, probably they would not even make it to the market, but the fact that they exist would put a lot of pressure on the large manufacturers that could not release with the latest-and-greatest firmware.
