Intel drivers are great for the most part. I'm not sure what you are getting at.
Prevalence of driver related faults will always be influenced by the marketshare of the hardware.
Vista usage (and thus faults) was heaviest around the time period of Nvidia's 8000 series products; a time when Nvidia's marketshare transitioned to nearly double ATI's after having trailed for many years.
It's no surprise that NV driver faults were so much higher than ATI driver faults, when you consider that most enthusiasts (the ones not just casually doodling on PCs but rather playing BF2 and CSS on their 8800GTs etc.) had NV cards and drivers running in their systems.
Raw pie charts like this often erode the context which helps to tell the story. I'm not saying NV drivers were or weren't trash at the time; it just makes sense to try and explain why things might have occurred like they did.