Sipadiver, it is easy to get almost any accessory here. Their case for the camera is not that big and sells for under $500 US. I know of no other camera with interchangable lens that is near that price.
While I don't use that camera, I do use both the LX-5 and their GH-1 underwater. We are talking apples and oranges here. I shoot mostly with the LX-5 (think the G12). It is far more adaptable for taking a variety of images.. I can shoot close up, or somewhat wide angle. Big things, little things. I use the GH-1 for either Macro (my water is not clear, so wide angle does not work) or wide angle when on a vacation. Lovely to take pictures, does each function much better than any Point and Shoot (I own a G10 and S90 also). But it is only doing one thing, so it should be better.
Why not go with a dslr? Well size and weight. My setup is half the size of an Dslr. But there is more. Fact is there are advantages and disadvantages of any system. In macro, a smaller sensor means more depth of field..which can be a good thing.
Taking images like this are hard with a point and shoot (using an add on lens, finding it, etc) and very, very easy with a dedicated system:
but when you see that lovely skate, all you can do then is take something like this:
I like both systems, but if you are going to take dedicated images, then the Olympus is the best size and cost there is. Going to use a point and shoot, and the field is fairly crowded.