When you look at the first "trial" Linux client then it was working like the win32/osx one, i expect the final client will work similar. If you don't remember:

http://store.steampowered.com/public...m_client_linux

That file was used to update/install the client. The win/osx installers are stubs only as well. So i don't see the point why the binaries should be Ubuntu specific, maybe the steam installer will be in the U repository but thats all.