Apps, even those that make very little profit, are great until you factor in customer service. I spend far more time than I'd like answering the same questions over and over again, even though I post several of those answers in the app description and on the website. Sure, I could do a better job of this, but most of my customers don't take the time to read the FAQ and go straight to the customer service email.

I can only imagine how many emails arrive for those with apps selling more than a few hundred/day.