Very interesting. It's pretty late here, but there seem to be a lot of arbitrary assumptions in that article. Example, a statement like: "It seems that B is at least as good as B-."
For the populations kept separate, nothing in regard to comparative happiness is "ethically bad" in an objective sense because of ignorance of both parties, in regard to the existence of one another as well as the less happy population being ignorant of a more happy population. In the example, one population doesn't realize its lower level of happiness, thus it doesn't realize a (much) higher one exists, therefore not creating an ethical problem. The other population (A) likewise isn't even aware of A-, so why who exactly would feel the ethical responsibility? It could be stated that ethics don't matter (practically, economically, and historically, that is) until a majority realizes something. Awareness is the key.
Dunno, i'm really tired so I might try to read again tomorrow. But overall, seems to be an interesting problem. Reminds me a bit of this episode:
http://en.wikipedia.org/wiki/Symbios...xt_Generation)
While we're on the subject, I'm pretty convinced that something like Utilitarianism, which out of many philosophies is one of the top ones I adhere to, will never be achieved without having a device similar to the Replicator in Star Trek. And even then, one would have to be freely available to every person in existence (and given the greed and power-lust ubiquitous in human nature, especially in hypothetical distant outposts, this seems extremely unlikely to ever truly be achieved.)