Frank, Thanks for the comments.
Secondly, thanks for posting those images, stunning to say the least.
If I dove in conditions that those images were taken in, I would be using a DSLR (I own a GH-1 and a 50D).
The minimum focus on the 9-18 is 250mm, the minimum focus on the XZ-1 is 1mm.... given that one is at 36mm and the other is a 28mm, the difference is something around 50 to 100 times closer. They don't actually compare.
Your ship image demonstrates where a dome and larger sensor really excel.
Dynamic range is a huge issue on a clear sunny day, where the difference between the bright sun and shadow covers a huge range. It may be possible to have that happen in really clear, shallow water, with a clear sky, but it is not common. For the most part water greatly reduces that effect. Just look at histograms and I think I have 2 or 3 images a year with too large of a dynamic range. On land, it happens all the time.
Small camera lens, interestingly, actually have much better resolution than their bigger brother, they have to to make them work with those tiny sensors.
My point about small camera's is that you can take wide angle, but going thru all that extra glass does have an effect. But being able to switch back and forth on a dive is nice.
In 10 ft of vis, for the most part, a wide angle setup is not that usable. One can get a few images, but for the most part they don't work that well. In 150 ft of vis, well any camera works, but there are some images best done with a dome.
But if one gets a Pen, with a dome, and a flat port, and buys a 9-18 and a macro lens, the cost is several P&S setups. And you can only use one at a time.
Two years ago was diving in the great barrier reef with a photographer for UK's biggest UW mag. Every morning we would discuss if this was going to be a wide angle day, or macro, finally on our last day he shows up with a wide angle, and says "I don't care what the conditions are, I am shooting wide angle". As it happened, we spent the first dive with Manta's and his images made anything I took look like junk...but the rest of the week was mine.