AFAICT, the Thermal Spec they give is the maximum recommended temperature that the IHS should be at for long periods of time. Intel aren't as clear as they could be about this.. they call it the "Maximum Case Temperature" in the P4 Thermal Management section of the site, but they don't mean that it's the max temp for the air inside the case/chassis. (The maximum temperature that chassis air used for cooling the processor should be at is supplied by the Maximum Recommended Fan Inlet Temperature.)
Naturally, your processor's not going to sputter and die as soon as the core hits 69.2 degrees Celsius. After all, the IHS is supposed to be a little cooler than the core at all times. If you don't have a way of accurately measuring the IHS temperature, you could always err on the safe side of things and use the core temperature instead. The obvious downside to this is that it'll be harder to stay within the Thermal Spec using core temperature measurements.
