Quoting PossiblyImpossible,
Right in between the Stardock avg. and the GPG avg: 80ish. Bingo!
Technically, right between them would be 83.
Also, it is important to realize that publishers can have a huge influence on quality. Stardock's commitment to quality by pushing the game back 2 months would not likely have been seen by the publishers of the low scoring games from GPG. Publishers can force developers to push out incomplete projects, as I am sure we all know. GPG appears to really average around 80 with a few outliers.