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But as far as getting the surface hot, they can withstand like 2000 degrees usually. You aren't going to melt them.

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This is correct. However, they can scratch and at that point, thermal shock (which you gave an excellent example of with the cold pan onto a hot surface) is a big concern. Even minor, hard to see scratches can be problems if pressed against a hot pan bottom for an extended time. In the lab, we usually placed an asbestos screen between a glass beaker or flask and an open flame to help protect against thermal shock, which could cause a Pyrex flask to explode. Not always, but the possibility was always there.