rationale for inclusion of hgroup in html5?

I have been trying to hunt down some data on the rationale for hgroup's
inclusion in HTML5
the only mention of rationale I can find so far is on the whatwg wiki [1]

"The point of <hgroup> is to hide the subtitle from the outlining
algorithm."

 there must be more than this right? anybody have pointers to anything, data
maybe on current use of headings for subheadings, any data on use of class
or id names to identify subheadings titles etc?

[1] http://wiki.whatwg.org/wiki/Rationale#hgroup_and_other_heading_elements


-- 
with regards

Stevef