Nah dude. I'm not sure where you got your info from, but Game of Thrones was edited with Avid. There's tons of press on how it was cut with a huge editorial staff on a Unity. I know of a handful of features that have been cut in Premiere, but the Coen Brothers' upcoming film is the only big one I can think of - and it works for them since they have a tiny editorial staff. Premiere may be the most common NLE worldwide, but not for TV/feature offline editorial.
About Speedgrade - I'm 99% sure it was a $20K application before Adobe bought Iridas. I don't know if you ever used Speedgrade before 2011, but it was the least intuitive piece of software ever. There were only a small number of good Speedgrade colorists in Hollywood since nobody wanted to learn such a confusing program, which in turn made post houses leery of investing in Speedgrade over DaVinci or Baselight. I worked at a place that primarily used Speedgrade at that time, and trust me, it was super frustrating. In 2011, Speedgrade desperately needed a new UI, and Adobe (who makes great UIs) needed an integrated coloring app, so the purchase of Iridas was perfect.