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).
100 seems an odd number to be a technological limitation, doesn't it? It's not a power of two or anything so it's not the size of an integer. How could technology have been limiting it?
S3 bucket names are globally scoped - ie. they are literally scarce resources.
Technology in the sense that it was a hard coded variable, but it was picked arbitrarily.
What would be a good justification? Is there anything you can do with 101 buckets that you can't do with folders one bucket?