No, Alpha still adds in features. Features can be added and removed all the way up until the game goes gold, there is no set stage where features aren't added anymore.
thats not true typically games as large as skyrim has a content complete mark at a few months before release to allow polish and testing, clearly you have never written code with a program as massive as skyrim adding or removing on thing could cause bugs all over the place. you must reach content complete to test effectively. on top of this you must go gold 3 weeks or so before release so the discs can be manufactured, boxed, and shipped to stores. so with 6 months until release we can chop off 3-4 months conceivable giving the game about 2 months where content is still being added, however i would put money on beth only polishing and only adding features already planned. Tell people to go make things on the whim of the community and the game would never get done.