[jsr]

Sounds like either thermal grease or thermal pad (not sure since you first mentioned a jelly like substance, then a white pad later). Direct metal to metal contact is actually a poor method of heat transfer as neither surface is truly flat enough to conduct heat efficiently as air is a poor heat conductor. A thermal layer is usually used to account for the lack of actual contact between surfaces. Not sure how far the heatspreaders and heatsink are. How can you tell they're far apart? Because of how much jelly there is when you pull them apart? You also have to consider the environment the part will be used in. Perhaps they wanted some space as an impact from the top would translate directly to a compression of the PCA beneath if they were in direct (or near direct) contact, which may happen in an RC application (i.e. if the car/truck flips over with no lid).