This is not true.
There are many programs that offer 40% rev-share, and in the end (with these programs) you will pretty much always end up with 40% of the amount the player deposited.
Example:
Player deposits $1,000 at Sun Palace Casino (Mainstreet Affiliates). After the player plays through all of his money, you will walk away with $400 (Mainstreet's default rate is 40%).
Player deposits $1,000 at Slotland. You will walk away with $150.
My suggestion would be to
not work with Slotland, as their commission structure sucks, and the games suck, too. To maximize your income, you should promote a casino that uses a well-known, popular software such as Microgaming, RTG, Rival, etc., and you should work with programs that offer rev-share rates of at least 25% to start.
I hope this helps.