Yeah, GoT wouldn't be nearly as big as it is without casuals. It's breaking ground, and the series finale could very well be the most watched episode of any fictional drama in the history of television. It's going to absolutely smash every record in the book. I suspect if it's legal to do so, movie theaters may even try to open up or sell tickets to air it on imax.
Speaking of that, since it's grown so big, it's basically become impossible to ignore, so a lot of people I know who have been "anti-GoT" because it's a "Nerdy dungeons and dragons kiddie show" started to watch it now, and I've been talking to a bunch of them about it and it's amazing how blown away they are by how great it is. All of them talk about how it's much different than they thought, they thought it was gonna be some cheesy Lord of the Rings spin-off type show.
One of the people I know who watched it was saying he really really had no interest and he's only watching it because his daughter basically forced him to. Long story short... he fully caught up(including season 7) in 3 weeks and it's now in his top 3 shows ever made.