I can't recall if the K5 has a 16:9 crop option for shooting, but even if it did, it would just be a straight crop of the full size image.
The difference between every other camera and specifically the GH1 and GH2, is that those cameras actually have a multi-aspect sensor (each corner of the sensor is a series of 3 edges, rather than a single corner) that allow native shooting at 3:2, 4:3 and 16:9 - the sensor is still getting a crop in each case, but a higher resolution is retained for each image, and the actual image will be different (given the same scene, the 4:3 image will have a taller actual view, 16:9 will have the widest actual view and the 3:2 image will be in between).
If you haven't already looked up the GH1/2 image sensor, google it, because it is definitely unique and something not offered in any other camera.
This is a good comparison - the right image is how any other cameras achieve a different aspect ratio - through cropping; the GH1 (and GH2) attain different aspect ratios by having a multi-aspect sensor, something completely unique.