Different scenarios. In the event above the poster already owned the vehicle and called to report that his vehicle had been damaged, (in this case by hail). If you are buying a vehicle and it is damaged then yes they will refuse coverage without an appraisal. But in this case the damage was reported and the insurer used that info to refuse coverage, (some other companies "may" have offered to continue comprehensive but at a higher premium). They did this because of the INCREASED risk. Same if a collision is reported to insurer you are an INCREASED risk.
Yes if your vehicle is damaged they will not give you comprehensive. I've bought old vehicles and had them refuse to provide coverage until I get it inspected to prove it is in good condition.