I found it... them, really.
http://www.sqlmag.com/Articles/ArticleID/19851/19851/pg/2/2.html?Ad=1
http://www.sqlmag.com/Article/ArticleID/20242/sql_server_20242.html
I'm not a "member" of that particular site so I can't see the whole article. What I glean from the two articles is that there used to be a difference in the early days and that there's really no difference now.
What is interesting is, if you scroll down in the 2nd article, you'll find that "PAD INDEX" supposedly makes the 0% and 100% fills even "tighter"... seems like they both leave 1 extra row without it.
--Jeff Moden
Change is inevitable... Change for the better is not.