Google seems to think that customers without credit card data are worth this: http://code.google.com/appengine/docs/quotas.html .

Be it $400, $100 or $50, AWS could (in my opinion should) go that extra mile and offer some option without requiring credit cards if it truly wants to take on GAE in this regard.

GAE has an advantage because it can put an app to sleep and wake it up on demand. So, Amazon's marginal cost of services is higher given that they must model the behavior of a physical box in terms of responsiveness. At a minimum, Amazon must maintain RAM allocation for the server, right?

It's also not even clear Google cares a lot about GAE profitability. When it first came out, there was only the free version, and the limits were there just to keep usage reasonable. As with many Google things, it seems like it was basically something they built internally for internal use, and then decided to make available to the internet for free.

Only after much clamoring by people who actually wanted to pay Google money for more usage did they offer a way to pay for higher quotas, almost a year after the initial rollout.