$40/pw is $2,000/yr... don't think it's unreasonable to ask what the plan is... And I bet they would try and look after you in some way if you are unhappy with their plan. I know I would in their spot! Referring 40 webmasters is unusual for 1 affiliate in my experience.... It would show them you are a big personal supporter of theirs at the very least.
I used to try and make money from referal commisssions.. but lots of programs seem to stop paying you for one reason or another over time... very frustrating.
*Edit: Oopsie... i see now you said 50 bucks per month... not sure why I read $40/week... must be too many drugs (or not enough)