I challenge you to go to any restaurant that has "unlimited refills", back up a tanker trunk and fill your truck. I don't think any court would enforce "unlimited" for that situation. I'm not sure this storage one is all that different
I think the answer is that Google did in fact target companies with exceptionally high storage needs. They were just assuming that everyone who had lots of data would also spend a lot on other services and that didn't pan out.
A better comparison is probably a restaurant promising unlimited coffee refills for life, forgetting to make it conditional on ordering food as well. Then some office worker who never eats breakfast turns up every morning for three double espresso refills.
In your analogy it would be Amazon setting up an S3 front on their corporate unlimited Google account. That didn't happen, it was just someone with more data than average. Google knows very well what the distribution looks like.