it's not as clear cut as that. it was never the heat the cpu's as a package produced that was the problem per se from my understanding, but rather a problem of switching those transistors on and off reliably at a rate of 5 billion times a second (5ghz). they have to deal with current leakage which is a result of power input, process size and and switching frequency. The faster they switch the more power they require to do so and the more power they leak. There's only so much they can do to combat that and making the process smaller only makes this problem worse because the current leakage vs power input is increased. Intel didnt know this, untill they tried to scale the pentium 4 netburst architecture. They famously said they expected netburst to scale to 10ghz when it topped out at 4 because of inefficiancies of the design, both in speed and power usage. Thats why they abandoned netburst and went back to developing the core technology.