In theory, it is entirely possible to design a digital camera that supports multiple aspect ratios, AND fully utilizes all the sensor's pixels in each ratio.
The Panasonic LX3, ZS3/TZ7, and GH1 all support multiple aspect ratios of 4x3, 3x2, and 16x9 without *purely* cropping, but each step to the right loses some total pixel count anyway. With the LX3, it's 3648x2736 (9.98 mp), 3776x2520 (9.52 mp), and 3968x2232 (8.86 mp). So for me the question is, would preserving the original count of 9.98 mp be possible, and if so, would that require a larger, heavier lens, and/or would that entail a necessary compromise in quality or performance elsewhere?
Maybe we should all campaign for the mfr's to introduce a slider to smoothly move from 4x3 to 16x9 with no "steps" in between. That would be the better solution.