From a longer interview:
WSJ: How do you get behind startups with no business model? With Pinterest, how do you get from zero revenue to a $3.8 billion valuation?
Mr. Andreessen: There are two categories of companies like this. You can guess which one I think Pinterest is in.
There are the ones where everybody thinks they don't know how they're going to make money but they actually know.
There's this kind of Kabuki dance that sometimes these companies put on where we're just a bunch of kids and we're just farting around and I don't know how we're going to make money. It's an act. Facebook always knew, LinkedIn always knew, and Twitter always knew.
Now, there are other companies that honestly have no idea. Like, they really honestly have no idea. You need to be very cautious on these things because one of the companies that had no idea how it was going to make money when it first started was Google.
That's an insightful take on the question.
Though notice how he manages to argue two opposing viewpoints and get away with not answering the interviewer's question about valuation! That was almost politician-like and very amusing.
Are these companies likely to have strong business models in future? Quite possibly. Are they therefore worth tens of millions, hundreds of millions or billions today? No one knows.