Generally, getting a case to use a camera underwater is expensive. The case has to be custom made for the particular camera, and it has to be full of waterproof push-through button-pushers for all the major controls. Digital cameras have helped a lot, since they can shoot far longer on a "roll" and things like zoom are electronic. They also sell in enough volume that some cases have gotten down to reasonable prices.
But more is possible because most modern digital cameras feature complete electronic control, either by USB or via infrared. This should make it possible to build a generic underwater camera case for whole classes of digital cameras of a certain size. The case itself can be very simple, with no holes or button gaskets. For cameras without infrared remote (or where the IR remote does nothing but a couple of buttons), a small USB to IR converter would allow complete control.
The box is simple, the real brains would be in an underwater-capable IR remote control carried or mounted on the outside of the case. It would need personality modules for new models of cameras but otherwise could be pretty much the same as well.
So you get a much simpler box and you get mass production because you can sell it for any camera. And you can keep it for your next camera. It's a bit bulkier, but that's about it. And it can offer more controls, even some controls that aren't even on the camera in some cases.
Zoom can be a bit tricky. You want to avoid glare off the plexi at the front when the lens isn't up against it. It's possible that might be designed to telescope when you change zoom settings, or the camera itself might gently move in an inner frame. Or it might just have a black bellows "hood" in the space between the lens and the view panel. This problem also exists in custom cases of course.
The same idea could also be applied to above-ground protection in harsh environments (snow, rain, dust etc.) for expensive cameras. There you don't need a pressure seal, just a thick bag with the same remote ability. Shoot happily in the rain.