Yeah, I don't think I'm all that special and I pirated the earlier seasons of GoT. The later seasons I watched legally, because by then it was available on a local streaming site I could well afford. If pirating wasn't an option it wouldn't have meant I would've spent the money to subscribe to a cable package that included HBO, (which would've cost a lot because you had to get some expensive bundle) I just wouldn't have watched GoT at all. So they didn't really lose anything from it.
And it's possible I may not have watched the later seasons legally either, because "eh... too late to get into this thing now."
HBO is a luxury thing and something like GoT could be the thing that'll entice people that could afford it and were thinking of getting it anyway to subscribe. The most relevant thing that influences their subscription numbers is the average income of the middle class, not piracy.