One thing of note is that Button's nearest challenger usually had bad race. If you look how much nearest rival needed to get out of Button's lead, you can note that Britain was the only race where that happened.
After Turkey: BUT 61, BAR 35. 2.6 per race
After Britain: BUT 64, BAR 41. 2.56 per race
After Germany: BUT 68, VET 47. (BAR 44) 2.63 per race
After Hungary: BUT 71, WEB 51.5. (VET 47) 2.79 per race
After Valencia: BUT 72, BAR 54. (WEB 51.5) 3 per race
After Belgium: BUT 72, BAR 56. 3.2 per race
After Italy: BUT 80, BAR 66. 3.5 per race
After Singapore: BUT 84, BAR 69. 5 per race
After Japan: BUT 85, BAR 71. 7 per race
After Brazil: BUT 89, VET 74 (BAR 72). 15 per race (title clinched)