Haven't found a statistical analysis, I will look more if I get time after work. But here are several more examples, and even an article discussing the issue with some GM's in the league who say the same thing:
http://www.sportscolumn.com/story/2006/8/21/224021/716
http://proxy.espn.go.com/mlb/columns/story?id=2521701 (ESPN Insider. Google this URL and view the cached page and you can read it.)
"You always had to make allowances," said another general manager. "It used to be you'd factor in a half-run difference in a pitcher's ERA (going from one league to the other). Now, it's more like one and a half runs -- or close to it."
Cases in point: recent free agent and trade busts such as Matt Clement, Carl Pavano, Randy Johnson, Esteban Loaiza and many other pitchers who have made difficult transitions from the NL to the AL. All have seen their ERAs rise significantly since coming to the AL over the last two years. Loaiza's struggles (3.77 ERA in 2005; 6.34 ERA this year) with the A's have been the most pronounced of the group.
http://www.boston.com/sports/nesn/wilbur/sports_blog/blog/2006/06/21/national_disgrace/
We may miss them, but it’s becoming more and more evident exactly why Pedro Martinez, Derek Lowe, and Bronson Arroyo are flourishing in the NL (a combined 20-9). Heck, Alan Embree, who couldn’t buy an out last season, has a 3.65 ERA with the Padres this year. Conversely, we know why Rudy Seanez and Julian Tavarez came to Boston in the offseason with pretty good resumes. John Wasdin could switch leagues and become a 14-game-winner.
I understand there’s a time and place for hyperbole and that we may have just crossed it. But think about it, while Arroyo leads the list of guys who are enjoying success in the NL after life in the AL (as are guys like San Diego’s Chris Young -- 6-3, 3.27 -- and Philadelphia’s Tom Gordon -- 20 saves, 1.47 ERA), Baltimore’s Kris Benson (8-5, 4.32) is probably the pitcher with the most success in making the opposite transition. Other than that, you have plenty of your classic Matt Clement, AJ Burnett, and even Josh Beckett struggles to fall back on as primo examples.
Mike Remlinger is dependable in Atlanta. Kyle Farnsworth is anything but in the Bronx.
If the GMs take it into consideration, it must be more than public perception. Like I said I will try to find something statistical about the whole league.