> 
> Because there are no namespaces in HTML?

In practice, that only matters if you are going to put the document
through a formal validator, but this is only going to be used in
machine generated blogs where the HTML is either generated by the 
machine or by someone who is not going to act on the validation
by the site owner.

If this attribute were inserted by hand, there would be an issue 
with authoring tools, but it is only going to be inserted by the
blogging software, although possibly removed by hand.