I've had three dells (all older core 2 duos), a core 2 duo MacBook Pro, a newer i7 MacbookPro, an older Acer, a much older dell (talking Pentium III here), an HP (AMD based), a Lenovo, various G4 and G3 based powerbooks and a couple I am probably forgetting. All of them have run long stretches of 24 hours/day 7 days/week and only two have had overheating issues. One was one of the Core 2 Duo based Dells that had known problems with heat cycles and soldering related to the Nvidia GPU even for people who didn't push them hard and the other was the i7 based MacBook which functions fine, you just can't use the GPU without the CPU throttling immediately. Some of them have done mining but mostly I have used them to run various BOINC projects but these push the CPU and GPU at least as much as mining does.

Most of them, with the two exceptions I mentioned, handled running at 100% cpu utilization and 100% GPU utilization for days at a time without issue.

The newest laptop I currently use (the i7 based MacBook Pro) is about four years old. The next laptop I buy will be a gaming laptop (perhaps an Alienware but I haven't decided and won't buy one until I really need one) because I know it will have decent cooling. Laptops having heat issues really seems to be a (relatively) recent phenomenon as manufacturers have pushed thinness and lightness a little too far. Otherwise, I've found that as long as vents are not obstructed, the fans are working as they should and they aren't in a particularly harsh environment, laptops don't have heat issues. If they do, like I said, I consider them defective (others may have different opinions but that's how I view it and I purchase accordingly). A MacBook "Pro" that costs thousands of dollars should not have to throttle the CPU just to run one of its two "mobile" GPUs at 100%.

Other than the defective Dell above (and it was defective, Dell even extended the warranty on that particular model), I have never had a desktop or laptop CPU or GPU die because of heat issues no matter how hard I've pushed them. I've lost more power supplies and hard drives than I can count and a few motherboards, but never a CPU or GPU. Even that Dell wasn't the GPU dying, it was crappy solder holding it on the motherboard. I'm sure that the higher heat does shorten the life of these components but it obviously hasn't been enough to matter if I'm still running them many years after they are obsolete. The desktops I've had I build myself and always make sure they have reasonable cooling. With laptops you kind of have to rely on the manufacturer (or take steps like you've mentioned). But if somebody else has built it, as with a laptop, then I expect them to do it right in the first place.

Sorry, don't meant to rant, this is just a pet peeve of mine :)