Nigel Melican, a well-known tea authority, busted a number of caffeine-in-tea myths, which he posted on Twitter. I gathered them here: http://39steeps.blogspot.com/2009/06/nigel-busts-tea-myths.html

Please note especially point 5, which is where this specific myth is addressed. It’s a rather long article on the Cha Dao Web site, which should not be missed. There are a number of very thoughtful comments that follow the article, in which Melican and Robert Heiss write extended correspondence that gets down into the details of caffeine research.