Grargar: It isn't. The game costs $35 and €25 on Steam, respectively.
Cavalary: Sure is a weird one then, and would be biggest EU discount here so far.
Train Fever: 20%
Shadow Warrior (2013): 16%
Halfway: 13.86%
Grim Fandango Remastered: 11.34%
Mount & Blade: 11.01%
Mount & Blade: Warband - Napoleonic Wars: 11.01%
Mount & Blade: With Fire & Sword: 11.01%
Gone Home (UK only): 7.5%
Double Dragon Trilogy: 6.68%
Guacamelee! Gold Edition: 3.34%
Mount & Blade: Warband: 6%
World of Goo: 1%
(Taking lowest EU price if multiple.)
Most of them a a result of the weak Euro and were more expensive than the base price when they arrived here. I think only Train Fever, Halfway, Double Dragon and World of Goo were cheaper right from the start.