If a movie is mastered in 4k, it is probably also distributed in 4k (but not always).
4k movies do not get distributed as 2k DCPs, because a DCI server should be able to playback 4k content in 2k, so if a movie is in 4k, it gets distributed as 4k. The same 4k DCP can then be shown at 4k resolution on 4k projectors, or in 2k resolution on 2k projectors. Also, it can be shown at 2k resolution on 4k projectors but noone in their right mind would want to do that (but some still do).
There are currently some 50 or so 4k features. Lots coming in 2013, some archival masters will probably get a 4k release also in the future.