its because Nvidia can't solder there chips onto PCB as soon as the chip hits 75+ constantly the heating/cooling stress causes a few pins to desauder and then it flopples.

Read http://www.theinquirer.net/inquirer/news/1004378/why-nvidia-chips-defective for a good summary.

Aftermarket cooling for the GPU helps a lot. When running VO my GPU never goes above 60, and idles at 45. By keeping the temperature range tight heating/cooling stress is substantially reduced, extending the lifetime of the card. You can't really do that on a laptop though...