Re: CoinTerra announces its first ASIC - Hash-Rate greater than 500 GH/s
Raw wattage isn't the whole story in thermodynamics. Your lawn on a hot summer day probably absorbs a couple KW of heat. Do you have exotic water cooling or install heat sinks on your grass blades to keep it from bursting into flames? 
Now that was a intentionally silly example but heat flux especially localized heat flux is relevant in the heat transfer requirements of the cooling system. This is why both HashFast and Cointerra are able to use OEM CPU coolers despite as you point out no CPU has a TDP of 300W+. They are designed to handle the much higher heat flux (W/cm2) present in modern CPU and cooling a large die with relatively even and low heat flux is less of a challenge.
Now that was a intentionally silly example but heat flux especially localized heat flux is relevant in the heat transfer requirements of the cooling system. This is why both HashFast and Cointerra are able to use OEM CPU coolers despite as you point out no CPU has a TDP of 300W+. They are designed to handle the much higher heat flux (W/cm2) present in modern CPU and cooling a large die with relatively even and low heat flux is less of a challenge.