I did a compilation of RPG .
The Elder Scrolls IV: Oblivion - Owners: 1,356,213 ± 63,221
Fallout 3 - Owners: 360,111 ± 32,649 (remember it wasn't a Steam game, it was GFWL)
Fallout 3 - GOTY edition - Owners: 1,363,168 ± 63,382
Fallout New Vegas - Owners: 3,290,460 ± 98,053
Skyrim - Owners: 8,281,789 ± 153,816
Final Fantasy XIII - Owners: 303,699 ± 29,986
The Last Remnant - Owners: 625,945 ± 43,019
Valkyria Chronicles - Owners: 269,697 ± 28,260
Mass Effect - Owners: 1,120,518 ± 57,495
Mass Effect 2 - Owners: 1,076,470 ± 56,359
DA: Origins - Owners: 474,482 ± 37,467
DA: Origins Ultimate Ed. - Owners: 942,781 ± 52,759
Star Warks KOTOR - Owners: 1,633,638 ± 69,344
Star Wars KOTOR 2 - Owners: 1,061,788 ± 55,976*
Divinity: Original Sin - Owners: 795,182 ± 48,469
Wasteland 2 - Owners: 410,342 ± 34,848
Dead State - Owners: 47,912 ± 11,917
Shadowrun Returns - Owners: 782,817 ± 48,092
Shadowrun: Dragonfall - Owners: 330,746 ± 31,291*
Pillars of Eternity - Owners: 226,422 ± 25,896
BG2 Enhanced Edition - Owners: 224,876 ± 25,808
Mount & Blade - Owners: 778,953 ± 47,974
Mount & Blade: Warband - Owners: 1,704,733 ± 70,826
M&B: with Fire and Sword - Owners: 964,418 ± 53,359
The Dark Eye: Chains of Satinav - Owners: 141,417 ± 20,469
Legend of Grimmrock - Owners: 850,821 ± 50,130
Legend of Grimmrock 2 - Owners: 95,824 ±16,851
Might & Magic X - Owners: 134,462 ± 19,960
Gothic - Owners: 159,964 ±21,769
Gothic 2 - Owners: 200,921 ±24,396
Risen - Owners: 607,398 ± 42,379*
Risen 2 - Owners: 959,782 ± 53,231
Risen 3 - Owners: 88,869 ± 16,228
Arcania - Owners: 317,609 ± 30,665
Two Worlds - Owners: 438,934 ± 36,039*
Two Worlds 2 - Owners: 496,892 ± 38,340
The Witcher - Owners: 1,718,643 ± 71,112
The Witcher 2 - Owners: 2,697,744 ± 88,901
*unreliable data