Sky will be advertising the launch of Sky Atlantic at considerable expense, and that, coupled with the the money it has invested in procuring programmes, will mean that they want to keep it exclusive for a period - an expensive ad for Sky Atlantic is also a free ad for Sky.
Once the dust has settled they will probably drop the price for other platforms and we'll see it on Virgin and maybe BT too. I fear that this won't be in time for season 5 of Mad Men, which means I will end up watching my favourite show on my laptop rather than my HD TV
Like Old Boy, this channel really appeals to me, but I'm not prepared to switch platforms for it. I still can't quite figure out why Sky didn't add it to the Sky Movies packages (that's how they premiered The Pacific last year) - I would have thought that would have driven more folk to take up more premium subscriptions and paid back quicker - but they've gone a different route, c'est la vie.