I didn't use a DSLR before, so for me starting with "Live View" was a natural progression of upgrading from a PnS. Plus being painfully nearsighted, I wear one of the "bugeye" HydroOptix masks, which would make using a viewfinder a bit more awkward, although probably not impossible. I have gotten to like using the viewfinder for above-water shots though....my glasses don't get in the way as much as the bugeye mask
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Basically after diving for a couple years with a prescription mask, and feeling like I had blinders on due to the combined FOV loss of an air/glass/water interface in addition to a corrective lens (I likely had less than 90 degrees FOV, and had so much 'magnification' effect I often dangled a hand below me to be able to tell how far from the reef I was) I'm addicted to the wide FOV of the HO mask, and don't really want to 'leave' that even when shooting. First motivation for me is the dive, the pictures come along for the ride. Maybe when I get more focused on photography specifically that might change.
I suspect that the primary liveview users will be those who switched from PnS after LV was available, and those who have tried the few near-zero-lag live view options...I don't see the Canikon live-view options out there now as terribly viable, and anyone who's used DSLR's (or film SLRs) underwater for years will not need or want the "crutch" as they're already used to the viewfinder.