Right it can be anything that is running so intensely like frames or stress. But games can have things accidentally of that nature, which means systems that aren't as efficient at cooling start failing in one game where they don't in most others. Like Star Crafts frames. As you mention it could be stress testing as well, what if I wrote code that made the core calculate in a manner that acted like a stress test but wasn't trying to be? It could have the same overall affect, and thus bad code. Then for systems that aren't ready for that can fail, that is what I was always getting at. There have been reports of things like this over the years, frames being the majority.
Again, you're just saying 'some games require 100% CPU or GPU to run'. Yes, that is true. And any system that is properly configured is able to run at 100% for any amount of time. If your system can't, the problem is your system.
You can argue a particular game shouldn't take that much to run, but that has no relevance to the fact that a healthy system can sustain 100% usage on everything for any amount of time without overheating, or crashing, or giving an error.
