
I wondered the same thing.  When he first mentioned it, I thought he was
just making a mistake but then he said it over and over.  And then in the
examples from other years, he gave stats for players from both leagues even
when only one league expanded.

So (since stats *NEVER* lie :-) ), I guess there is an effect on both leagues
because the expansion draft takes talent from both leagues equally making 
every team in both leagues dilute their major league talent by calling up
players that, normally, they would not have had there not been expansion.