KQED just ran a short piece on ROVs and the future of ocean technology, From Alvin to Robots: Changes in Ocean Science. Some of my favorite quotes:
"It's obvious. ROV's are just better."
"We can give more people opportunities than we can with a submersible. It's really a no brainer." -Bruce Applegate, Scripps Researcher
"Science needs to be inspiring. Kids need to get excited about exploration so that they'll grow up and do more science."
The moral of the story, for me, is that we need robots AND humans to explore the oceans. It's not an either/or situation, it's a more of both situation.