I have noticed that, even if i enjoy other games, most of the big hits in my pc gamer's life have mostly been published by the same companies:
1. Blizzard: Diablo1 - Diablo2 - (soon Diablo3) - World of Warcraft
2. Bethesda: The Elder Scrolls (Morrowind & Oblivion) - Fallout
3. ID: Quake 1 & 2 - Doom 1-2-3 - Wolfenstein
And you, have you already noticed something similar?