Earlier quoted context omitted.
That used to be a hard technological limitation but they fixed it a few months back. You should be able to get more now (but you have to have a good justification for it).
What would be a good justification? Is there anything you can do with 101 buckets that you can't do with folders one bucket?
Requester-pays billing (http://docs.aws.amazon.com/AmazonS3/latest/dev/BucketBilling...) for more than a hundred clients, static sites served through CloudFront, etc.