Let's suppose that your sales are going quite well for the summer time. Let's say that at the end of the day you have an average of 100 daily sales; in 30 days you will have 3000 sales; let's suppose that the product costs 29 bucks; that means that at the end of the month you have 87,000 USD in sales; applying the standard 8% processing fee will result in a 80,040 USD in your pocket.
Now, the little question is how can you generate more revenues with the same number of customers :)
The answer is quite simple: by selling additional services. For a small amount the customer can opt in to receive a backup CD along with the order or he can obtain to increase the download availability for 24 months. Now, adding a small profit of 5 USD on top of 70% of your existing 3000 sales, the final profit will be 90,540 USD - meaning that an additional 10,500 USD monthly profit just came up :)