Not to be disrespectful at all, but in my opinion choosing a digital camera system based on which underwater strobe it can fire is absolutely nuts.
I don't agree with this at all. DSLR systems underwater are very expensive (as I'm finding out) and strobe performance is one of the biggest factors influencing your pictures underwater. Because it is more expensive to house an underwater camera--more expensive than the camera itself in most cases--anyone persiong this option would naturally put pretty heavy weight on underwater performance. This is true even for the serious ameteur.
I agree that given TTL performance and lens options available the S2pro is probably the best DSLR for underwater. Frankly, I knew I could never afford this camera so I bumped it off my list of considerations. There is more to consider for an underwater system than TTL:
1) cost. I went with the D70 because with the kit lens and less expensive housing it will probably be about $1000 less than the low price S2 configuration. This includes:
Camera body: Fuji $1500 (ebay good deal) D70 $1000 delta $500
Basic Lens: Fuji Sigma 17-35 ~$400 D70 kit lens $300 in kit delta $100
Don't mention nikon 17-35mm/17-55mm $1600 wow!
Housing: Ikelite S2pro $1500 Ikelite D70 $1200 delta $300
delta $900 (this is with buying the body on ebay, list price is much more)
2) The s2pro shoots huge RAW files. I can take more pictures with the D70. Or put it this way, my minimum size 2-dive card is cheaper with the D70.
3) The ikelite s2pro housing is huge. The d70 is more travel friendly. Plus the camera itself is lighter.
4) battery performance. The s2pro uses 2 sets of consumable batteries. I suppose that you can get rechargeble AAs but the CR2? Nikon uses one simple rechargable that seems to last forever. Way more than any 4-dive day. My experience was ~2-300 pictures with review and internal flash and lots of playing with menus topside.
5) speed. The D70 is faster than the s2pro
6) TTL. The s2pro has an advantage now. But I'm hanging my hat that Ike will crack ittl and provide a retrofit kit. I hope. But manual isn't bad and I wouldn't use older, non-digital strobes anyway. I love the recycle time on my DS125.
We'll have to see about photographic performance once someone gets a D70 underwater. So far the S2pro is a proven champ.
So, the Fuji is a great camera. If I could afford one I probably would have it instead. Then again I'd rather have a Canon 1ds too. But I think there are some good advantages to consider on the D70 too.