The problem with these arguments is no one ever talks about
- what components?
- how hot?
- what does "death" mean?
The biggest killer of electronics equipment is almost certainly obsolescence. I've got a whole bunch of computers in my attic (G4 iMac, AMD Sempron tower, etc) in my attic as well as a PlayStation 1, a PS2, digital cameras etc etc. All in perfect working order. Just obsolete.
I guess the 2nd biggest killer for portable devices is user damage:- droppage and Coke, general abuse. That's how my iPods and phones die.
The 3rd is probably mechanical or power system failure. hard disk, hinges, covers, keyboards etc etc. That's why I seem to get through 1 printer every 2 years.
Then component death is probably a distant 4th. How much of that is heat related is highly debatable. But on these forums we only see a very tiny number of logic board deaths against loads of threads on dead batteries, LCDs, mechanical stuff, droppage & coke, HDD. Whether that constitutes evidence or not is hard to say. Interestingly many of the logic board death cases are 8600 graphics chips failing. This is a heat related death but it was IIRC down to poor quality control during manufacture of the solder bumps - a latent defect. Similar problem to the XBox360 RROD.
Then the "what components" and "how hot" debates are interesting. The Mac's cooling system is IMHO well designed. It conducts heat away from the CPU and GPU straight to the edge of the case & dumps it straight into the air (in contrast to many other laptops which dump the heat into the case and then suck it out using fans)*. Because of this your Mac's "components" don't get very hot. Download iStat Pro and take a look. Even redlining my CPU, the case only gets up to 30 C; the HDD in the low 30s. Take a look at the Northbridge. This is in direct thermal contact with the heatsink. And yet it only gets up to about 55 C on my 13". Other components not in contact with the heatsink will get to nothing like this temperature. I'd guess at about 40 C. Which is peanuts for a component rated to 80 C. It won't affect their life materially.
The CPU and GPU do get hot, but the CPU certainly sits well below Intel guideline temps. And Intel is the best in the business. They're not going to let you cook your CPU. Remember also that some of Apple's customers take a MBP and redline it 24/7 for weeks or years. We had a guy on here from Weta who was doing renderings for Avatar on a MBP. Think what his CPU has been through. Also I am pretty sure that Jonny Ive has got a whole test setup of MBPs going through torture tests (or "accelerated life testing" as we used to call it). He has probably got Core2Duo MBPs that have been redlined for >10000 hours, probably 5 years' use for even the most ardent gamer.
Now of course some overclocker will come on here and say they cooked their Pentium 4 by redlining it with no heatsink. Of course if you run your CPU up to 130 C it will fry. That's the "how hot" part. But if you obey the manufacturer's spec sheet it should last a long, long time.
So I'm with miles01110.
Incidentally I guess that's why cooling pads don't work very well on MBPs:- the bottom case doesn't get very warm, and there are no air inlets there, so blowing cool air over it makes little difference.