Think just that 1BTC is equal to 1BTC, not to its value in USD. Take as an example what happens in this forum with the price of VIP account: it was 50BTC since the beginning and it remained 50BTC, no matter the value of BTC in USD. Because the price was calculated in BTC and not in USD.
Yes it did, but also who is buying VIP now? Nobody! Under normal circumstances this would mean the end of the business and bankruptcy but bitcointalk has other sources of money (ads) so it really doesn't matter if people buy VIP or not. It serves as a statement not a real business model.
In real world who would be able to not lower the price despite nobody buying your product? Only a very rich or a very stubborn man.
Fiat value is important because fiat money means goods. If fiat is not important then give me 1 BTC for a gold ring. You'll ask for the value of the ring and I'l tell you pure gold, authentic, one diamond. Does it mean the ring is worth a bitcoin or not? How are you going to value it?