In all cases the user is the customer. Some customers pay with real currency (e.g. those who have enterprise accounts), others pay by loaning a few thousand pix

In all cases the user is the customer. Some customers pay with real currency (e.g. those who have enterprise accounts), others pay by loaning a few thousand pixel-seconds to advertisers. It's very much in Google's interest to encourage task-specific protocols, because they can be attached to subscriptions, and subscriptions are denominated in real currency. If Jane Smith knows that GAE has good support for syncing her calendar to her iPhone, she's more likely to use it as her company's email/calendar/documents provider.