It seems that the screen of the iPhone 6 and 6 Plus aren't infallible to the effects of a drop test to a hard surface. A drop test from the guys from Android Authority showed the iPhone 6 and 6 Plus making it through the drop test with their screens unscathed and just some minor scuffs on the sides of the phone. However a similar test from PhoneBuff shows how the iPhone 6 and 6 Plus respond to being dropped onto a hard pavement. The iPhone 6 Plus suffered more damage compared to the iPhone 6 owing to it's larger size.
At the end of the day, it all boils down to being careful with your device and using a case to give your phone more protection in the event of a fall.