Of course, You are absolutely right. The author said he had no idea how to value his work and I was thinking... Hmm, he might try to use financial math formulas such as the NPV as help. If the game makes $9000 profit per year at a discount rate of 3% you could value it:

    $8738 ... (makes profit for N years, where N = 1)
    $17221 ... (makes profit for N years, where N = 2)
    $25458 ... (makes profit for N years, where N = 3)
    $41217 ... (makes profit for N years, where N = 5)
    $76772 ... (makes profit for N years, where N = 10)
    $133897 ... (makes profit for N years, where N = 20)
    $284390 ... (makes profit for N years, where N = 100)

And no software is able to make profit for 100 years.

(disclaimer: my calculation might of course be wrong, I didn't put much thinking into it)

There are few who can make this happen. If you're not minecraft or a subscription/in-app-purchase game, you're out of luck.