You need to take into account the time value of money as well. While average return may be 10%, you're putting up the big capital right at the start and are getting 20% of that back each year.
But it's more like a lease of the ATM rather than you owning it, the ATM is only woth 10% of original cost at the end of 8-10 years. Therefore, it isn't really a 20% return.
