In a declining market, product cycles contract to maintain sales revenues

Well, I'm sure we're all delighted to hear this:

http://www.wizards.com/dnd/Article.aspx?x=dnd/4ll/20120109

15 years from 1st to 2nd edition
10 years from 2nd to 3rd edition
8 years from 3rd to 4th edition
5 years from 4th to 5th edition.

6th edition in 2015/6 anyone?