I agree, it's economic migration of a 'I can do better somewhere else' kind, more than a "I can't survive here' type.
I believe the same thing happens in Australia but the target is the US. Certain bright talents leave because they believe they will do better as a scientist, screenwriter, financier, musician, or whatever, in the states. I once met a guy on Wall Street from AU, he said to me he could have done well as a "big fish in a small pond" in Sydney, but knew he's make a lot more dough in NYC. We almost certainly have lower taxes on the ultra rich but I'm not going to go check on that.