The last piece of the puzzle is heatsink mounting hardware, and where those holes in the PCB are fixed. Each CPU class works with its own set of requirements in that regard, and the heatsink retention mechanism has as much to do with the size of a CPU cooler as anything else. In the image below, you've probably already recognized the four LGA775 mounting points spaced around the pinless CPU socket - these are the only points with which the heatsink can use to apply the necessary loading forces. That force is about a 40lbf static load in most cases, but may be as much as 70lbf.

The two translucent pieces of plastic directly around the CPU socket are keep-out areas that represent the electrical components which will be mounted into that location on the motherboard. During simulation, these components may restrict the exhaust airflow of a heatsink, so this is why they are replicated on the Intel 'TGRVP MTB' test motherboard as well.

Thermal Integration had assembled a basic 'live system' test case to illustrate how the company proceeds with real world evaluation of it is heatsinks in an environment where more than just CPU heat load comes into play. Using a Yokogawa chart recorder and at least five thermocouples, a specified heatsink could be evaluated when the heat output from adjacent videocards, chipsets, the motherboard, and power supply added into the mix.