The problem occurs when the GPU is suddenly stressed hard, and then suddenly is idle afterwards (and repeated often).
The solder cant handle hot->cold->hot->etcetera cycles, and cracks, causing the gpu to lose connection with the motherboard/gpu daughtercard.
This is due to laptops running hotter than desktops AND the shitty solder Nvidia used.
You're either lucky, your Dell has a great cooling system OR you never really stressed the GPU hard.
Portal 2 was all that has been played on it, so no great strain there, and it did keep remarkably cool and quiet.