That's because in those videos the factory thermal pads (1 blue strip, 1 grey strip) were stuck to the GPU plate of the heatsink assembly, so exposed VRAM looked like there wasn't anything applied. They're
supposed to be covered with the correct thickness of thermal pad (usually 0.5mm or 1mm) and as alternative option, you can use thermal paste. However, if it's not making contact with paste, 1mm thermal pads will be the replacement.
In this video at 57:50, you'll see exactly what I'm talking about. There's also 3 more tiny thermals pads (if you look closely) with 2 on the surrounding FETs near the choke, where
that thermal pad is still on the GPU heatsink (directly below the blue VRAM thermal pad).
EDIT: attached PIC for reference.
https://www.youtube.com/watch?v=2WJqpLoncCw&feature=youtu.be&t=57m50s