I am looking for information on desktop software purchasing trends in
order to determine if desktop software being sold at retail, brick &
mortar, is holding steady or declining.  I need some information or a
report that will give me some insight into the purchasing habits of
software purchasers as a whole.  Are people increasingly buying online
or to people still buy in stores?

My suspicion is that retail, shelved product sales are on the decline.
 I am looking for a report or a study that can tell me the trend.