Well, its quite true but really depends on what's inside.

If it has dedicated gpu from 1yr ago, they still run the gpu all the time. Newer ones allows switching between intel hd and gpu.
I bought a 2nd hand Dual Core Ultra Low Voltage and very surprised to find that its not as hot as my previous acer with 8600gt despite having it lay on my bed blocking the ventilation hole. The previous one would cook my eggs if I had them on my laps for too long.