Yes, there was a dotcom bubble, and now here we are typing messages to each other on the Internet. (Not only that, but on a distributed platform on the Internet!) The dotcom bubble marked the birth of a new technology, and there were a lot of companies that went bust in the frenzy. But those who survived and thrived continue to change the ways that we live today.
With Bitcoin and other distributed networks, we are witnessing the emergence of another technological leap forward. From what I have seen, Buffet and economists like Krugman fail to see it as a technology with potential, instead using the current paradigm to evaluate it as a static thing, assuming that the world will never change. They were wrong then, and they are wrong again now.
RE: Why Warren Buffet Doesn't Understand Cryptocurrency