Countach,
I'm ambivalent about the need to unscrew the crown on my SCB2.
You have me thinking though, and what you say makes a LOT of sense, especially the example of having to wind your watch, outside, during inclement weather.
What's interesting is that Lum-Tec offers another watch -- the BULL A16H -- with an almost identical movement (ETA 6497-1), and it has a diamond-seal crown, but lacks the additional screw-down feature. The AI6H's "glamor shots" are distinctively nautical, and feature it perched atop driftwood and dressed up in a rubber drive strap.
Both watches are rated "water resistant" to 100 Meters.
I'm not sure why the SCB2's screw-down crown wouldn't provide enhanced water resistance, but -- now that I think about it -- it'd probably be nice not to have to bother with threading and unthreading the crown, particularly if what you say is true about that causing wear to the sealing system.
Maybe Chris or Bes can clear up these questions??