This mirrors the failure rate of venture funded startups. About 70% of venture funded startups simply fail. Everybody loses most or all of their investment. Another 20% "break even" either through getting bought out at a discount or having assets sold to cover creditors and investors. 10% get to a successful exit where the investors get their money. This one winner in ten also has to make up for the losses from the other nine.
So I am going to say the Vitalik was being optimistic. Take away the frauds and stupid projects just grabbing for money and you already lose a big chunk. This is still such a new and rapidly changing technology that I would not be surprised that even plausible ideas and projects will fail at a higher rate the VC funded start ups.