Not only that, it's an average, and one has to take into account the losing streaks where the income is negative. It does not always cooperate and come after the winning streaks either, which compounds the problem when one os looking for reliable income. Long term is key to planning.
Flash probably assumes he is playing a strong counting system. I don't know what you use but his numbers look right to me. Just avoid lousy rules and pen and you are good to go.