Kevin said it above: it is not about being cheaper, it is about the camera. Leica.
The thing is, with digital cameras, Leica cameras will not keep on ticking forever like a film M. You spend thousands on a Leica camera, but digital is a great equalizer; odds are that your uber-camera will last less than 10 years, and then it is not repairable anymore. This is valid for all digital camera BTW.
In the end, your camera will be in a waste filler, or acting as a paper weight. Sure, if you have money, buy whatever you want.
What I suggested above was, say if you already have a Leica X, why not buy a waterproof housing? If you don't have a Leica X, why not buy it plus the waterproof housing? Kevin forgot to add in his review that this waterproof Leica is a Leica X in tough disguise.