My research on this was finished June 2, 2010:
Team Competitive Analysis Based on Runs: 1903 - 2009
It contains supporting data and graphs.
For those of you not inclined to read such a document, here is the final conclusion:
"In EVERY case, the records are closer in the last ten seasons than in the five most disparate seasons."
So why do baseball people like Bob Costas continue to repeat incorrect and unsupportable positions? I guess it's a baseball heritage: never let facts interfere with bias, superstition, legend and general purpose stupidity.
George Steinbrenner died three days ago, the morning of the MLB All Star game. All day there was commentary about George Steinbrenner, much of it lame attempts to not state criticisms that some had long repeated. They wanted to find something nice to say about George Steinbrenner, usually retreating to some sappy story of George's philanthropy.
George was called a patriot, leader, innovator, blah, blah, blah. What a bunch of junk. However, the one thing that they could not resist dredging up was the incorrect idea that Steinbrenner had ruined MLB competitive balance. He did not.
Steinbrenner was a buffoon. His only positive attribute was that he would spend, almost unconditionally, to improve the team. The other owners would not. Steinbrenner spent more and for a longer time than any owner. That is why Steinbrenner is the best owner of all time: MLB, NFL, NBA.