CBP lists countries whose citizens can apply for GE.
In the spirit of "reciprocity" shouldn't ALL of those countries allow US citizens enrolled in GE be permitted to sign up for a similar program allowing expedited entry?
[Case in point, Switzerland is in the list, but offers NO equivalent system for US GEers to enter. Generally (but [B]not always) entry into Switz. is pretty quick.]
Before you get too hung up on "reciprocity" it might be instructive to look a little closer to home. Australia for some reason gives GE expedited entry but doesn't get it in return.