[abritishguy]

Before the pricing change app engine did not support concurrent requests to a single instance for python. As a result, applications used many more instances than they needed.

When using the calculator this would make the price increase seem enormous to many customers. When concurrent request support was added (it was available to trusted testers at this time) all a user would have to do was add "threadsafe:true" to the app.yaml file to enable it (assuming their code wasn't doing anything silly).