Question: monetizing a google app engine product.
ChrisF told me that this question would not have been on topic, had it been asked on WebApps.SE. While I believe I understand the points made on Are API questions on topic?, I don't am unclear why this question would be considered to be a developer asking how to use Google App Engine, rather than a Google App Engine user asking how to use the site. Campaign Monitor, for example, has a developer side (API, libraries, etc.) and a web interface, the latter being the mechanism a user would probably use if they wished to create clients with their own billing.
Part of my understanding of this distinction is based on Where does my git question go?.
In short, I'm unclear exactly where the distinction lies between a developer asking how to use a web application and a user of that web application asking the same question.