Apologies mrskitcatb that I didn't reply sooner. To be honest, when I first read your post I felt I needed to give it some thought before I replied and then it got buried. FJT's answer really gets to the crux of the matter - we do not have unlimited funds to spend so we always have to prioritize our spending on what gives the most benefit to the most members. And indexing more books/magazines and adding new features would I'm sure be most members preference to giving a dollar or two back for referrals.
We also hope that if people love our service they would want to spread the word to friends and family who love to cook without needing an incentive. It's like if you see a great movie or read a wonderful book - you want to tell others so they get the same joy, you don't need the movie producer or book publisher to give you payback.