The default namespace is the empty string, similar to java's default package. Namespaces allow tables to be fully qualified. So, tables in the default namespace are fully qualified without a namespace prefix. The problem is, that doesn't show up well in the shell when we list namespaces. The string "(default)" was chosen as a placeholder, because we can't show an empty string (Eclipse, and other IDEs do something similar to show the "(default package)").
Do you have a suggestion that is more intuitive? One option might be to have a separate flag "--default-namespace" to expose it more obviously.