Why does that really matter? If I sold chocolate covered bagels, and I was the only chocolate covered bagel store in town, do I have to serve you?
Or, if you wanted to open your own chocolate covered bagel store in the only mall within 30 miles, does the mall operator have to lease you space?
As a developer, I find the situation painful, but I think Apple views the appstore as their mall, and they want to control the image of their mall by holding the store keepers to a certain standard in order to promote a certain customer experience.
Depending on the country your store is in: yes, you would have to serve me unless you have a very good reason not to (like I'm a returning thief or troublemaker).