I also have been considering a "tough" camera and have looked like you at the Nikon AW100 and the LUMIX DMC-FT4 which are similarly priced?
After extensive review reading I ruled out the AW100 as it seems to suffer from lens fogging issues so that was enough to put me off that one?
The Panasonic one also seems to have a fair share of bad reviews and the image quality compares to a much cheaper none tough version?
Finally like you I looked at the DSC-TX20 which is a nice pocketable size and seemed to tick all the boxes? The only downsides that seem apparent are that you could get sand/grit caught in the sliding mechanism if you use on a beach etc which could scratch the camera? Also it not exactly rugged build quality?
This doesn't bother me as I won't be throwing it around and just want a camera for when out walking the dogs etc that will stand getting wet etc ?
The reason I have not bought it though is it not physically in stock anywhere to see it in the flesh? Also there is a new model apparently being launched next week at the CES show called the DSC-TF1 ( rugged, 16MP, 4x zoom )
So I am waiting to see what price point it is set at and if the other one drops in price making it a bargain?