a quick google search came up with this:
http://www.iwc.org/world_whale_news/whales-1-3.htm
I think the problem is that whilst freedivers spend comparatively little time at depth, whales spend an hour or more? So the breathed air is being absorbed into tissue / bloodstream for some time. Also the volumes of air in a whale lung is much higher than a freediver.
I don't know, I'm guessing. I think time has a lot to do with it - when submariners escape from a sub (and it's been done from 200m) immediately before they leave the sub they are able to plug in a reg to the air supply on the sub. They must in effect go from surface pressure (in the sub) to 200m (hatches opened) back to surface in a very short time. I had always assumed that if a freediver took a single breath off a DV at depth, they would immediately have to follow a deco schedule. Perhaps a very fast, breathing out ascent (to prevent barotrauma) would be feasible as long as they weren't hanging about at depth?
[edit]sorry for the garble, it's a stream of consciousness aided by too much caffeine and lemsip in my system[/edit]