Actually, the post says it explicitly that this 20% includes only failures. --> "... entrepreneurs who previously failed have a 20% chance of succeeding."
This statistic wasn't there but one could imagine that it would be higher than 20%. Also, keep in mind that success is a subjective term -- for some people it's when you make $1M, break-even or get acquihired, for others it's at least $100M or $1B.
