Namespaces are a concept used in
XML.
They are required because the X in XML is for extensible. An application of XML will typically involve defining a set of new tags. The concept of namespaces ties a set of tags to a URI for uniqueness. Even if two separate XML applications use the tag <key> to mean a musical register or a computer button, they will be segregated by being in a different namespace.
An XML document may have a default namespace for all its tags, which may be overwritten with a usage like <computer:key>.
So in XML namespaces are A Good Thing, but for e2 node titles they are very unhelpful. In XML we try to structure information, in E2 we like to break down the structures.