yes, we are aware of that. Actually, the namespace was invented long before we knew how to access resources under www.humanbrainproject.eu and I am not sure we would actually have the permissions to store something there. However, namespaces in XML are just names. You can craft names as you wish, you only have to follow a very simple syntax, namely that these names should be valid URIs.
The fact that the schema is unaccessible simply means you have to tell it to your editor explicitly in order to get tool support. Or the tool is clever enough to read that information from the XML file (all experiment data have the schemas referenced).