I have to agree with Herbko that this camera is an entry level one and should be compared to 350D (370D?) and D70 (D80? or D50). Although these recent models are cheaper, they started from the same level (around 1000 euro) as I remember. The street price of sony alpha will fall soon. (I've seen body and kit lens for 848 euro few days ago in Germany)
And I also agree that the difference of quality is not much and I really don't care even 6M vs 10 Mpixel differences.
Regarding lens selection Minolta has some fine glass (Sony rebranded some of them) and Zeiss will produce also some high quality lens (not really for underwater photography but indirectly, yes).
What can we consider for UW photography:
Wide angle:
16mm Fisheye (designed for film camera, but not bad. Not as good as nikon 10.5 FE)
Sigma 15mm FE (similar)
Tokina is on the way to release digital FE
http://www.tokina.co.jp/news/4961607atx107news.html
It's not clear whether they will support sony or not.
11-18 mm
17-35 mm (good quality zoom but not really wide)
Macro
50mm and 100mm macro have legendary picture quality. According to independent tests Minolta 100mm macro is better than similar C and N lenses.
Sony just rebranded this two.
But I have to admit, they are not as fast (focusing) as the Canon (or Nikon) rivals but they are not so bad.
3rd party lenses (Tamron 90mm, Sigma 105mm)
The availability of UW housing is dependent on the selling statistics, which highly depends on the marketing and Sony will surely load lots of money into it.
Cheers
Marcell