I love my Samsung NX200 and use it often. My two-year-old Pentax K-x was down for a couple months after getting a dirty sensor at Morro Bay, but is now good-as-new. The NX200 is the superior camera, but I have used the K-x almost exclusively over the last few days.
The NX200 has almost double the resolution as the K-x, but in a smaller, lighter, and easier to use package. There is no doubt that it is indeed the better camera.
Why would I use inferior equipment when I have something better at my fingertips?
The NX200 does what the K-x does but better; however, it is not better in every aspect. The K-x has a little less noise at ISOs 3200 and above. I rarely use those ISOs (and certainly not for anything serious), but I would grab the Pentax over the Samsung in that situation. I own more lenses and filters for the K-x than the NX200, so that might be another reason to choose one camera over the other (although so far that has not been a reason).
The reason I have grabbed my K-x and left the NX200 in the camera bag is that Pentax gave their camera some tricks that Samsung did not. By "tricks" I mean creative post-processing that is built into the camera. I can do some things easily and fairly quickly with the K-x that would take significantly longer to do using software on my laptop.
Pentax included some pretty good photo editing software inside the K-x that allow you to do some creative things. Common post-processing functions take longer when done in camera, but some of the more exotic edits can be done much quicker.
The key to keeping the K-x an important tool was finding what it does uniquely. I can still get good use out of it by choosing it when I want to exploit those creative features. In this way, the camera gets new life and I create better images.