Evidence? You can make statements like that as much as you want but without any documentation proving your point, it's invalid. Hardware is designed to take the heat, and macs are no exception (regardless of model).
Ive had two MacBook Pros killed by hand break heat issues, and i have a friend (the one who introduced me to hand break) have an iMac killed by it, both of us were told by the Apple store we had them fixed at (thank god for apple care) that the issue seems to have been caused by heat, and we needed to make sure we had plenty of ventilation around the exhausts of the machines.
Also the 1st generation time capsules, the one that had a 75%-80% failure rate and apple eventually had to replace, had an issue where the capacitors in the PSU and/or the hard disk would fail suddenly due to heat stress (this was due to BAD design, a tiny plastic sealed box with a PSU and HDD is going to get HOT, but apple as usual would rather it looked pretty than have decent cooling)
The same design flaws can be seen in the iMac, to keep it pretty and thin the HDD is in the middle of the unit, instead of being near the edge where it could be cooled easier (and replaced easily by being in a removable caddy)
and as far as hand break goes, the Mac Mini and iMac heat sinks are around 1/4 the size of a normal desktop heatsink for the equivalent desktop CPU, if you think that doesn't impact cooling efficiency your mad.
Thermal limits are giving by manufactures as a guide, running at that limit all the time will reduce the life of the components, thats simple physics, drive a car at its top speed it will do all the time and you will wear out the engine/tyres/breaks quicker than if your drove at the speed limit, same with components thermal limits, run at them all the time and your chance of failure goes up exponentially.
Also, do you know that the thermal limit of the CPU might be 105c, but the HDD is probably around 65c, as the case and heatsink fair to get rid of that excess heat, other components heat up inside the case beyond their thermal limits and again , your chance of failure goes up.
Handbreak is a machine killer, its not a case of IF, its a case of WHEN, if you run it without throttling your playing the thermal lottery on all the components in your system, eventually the weakest one (failure is likely in this order, a capacitor in the PSU, a weak solder point, the HDD, or CPU , if your on an iMac you might even discolour or damage the screen from behind the hot-spot)
Breaking news! Desktops don't use notebook components!
Except the Mac Mini and iMac are both escentially laptop computers in a desktop case as far as motherboard, cpu, gnu and ram are concerned. They simply don't have the space required to house the heatsinks needed for desktop components,
