A more accurate assessment would be that much of this "value" never really existed.
When someone invests $1,000 and within a year the stock goes to to $20,000 and then loses all its value, it is invariably reported as a loss of $20,000, as though $20,000 of value ever really existed. The actual "loss," of course is $1,000, plus a reasonable one year return on investment.
This is the type of loss many of the Enron employees suffered, and is is different only in degree from a Vegas gambler who starts with $500, is momentarily up to $50000 and then loses it all.
I agree somewhat with your statement, however a drop in a companies equity could affect their credit rating which would make it more difficult to borrow money to conduct their day to day operations. This, I believe, is what could rattle the market.