Honestly you're under rating the ability of these foreign guys to draw the US is the biggest but it seems your suggesting the gap is a lot bigger than it is.
2004
Kenta Kobashi
Pro Wrestling Noah
2005
Kenta Kobashi
Pro Wrestling Noah
2006
Místico
Consejo Mundial de Lucha Libre
2007
John Cena
World Wrestling Entertainment
2008
Brock Lesnar
Ultimate Fighting Championship
2009
Brock Lesnar
Ultimate Fighting Championship
2010
Brock Lesnar
Ultimate Fighting Championship
2011
The Rock
WWE
2012
The Rock
WWE
It's wiki
http://en.wikipedia.org/wiki/List_of_Wrestling_Observer_Newsletter_awards#Best_Box_Office_Draw but the stats should be available elsewhere.
These are the stats for the biggest draws over the past 6 years according to wrestling observer (ignore the UFC ones as that's neither here or there as Brock wasn't pro wrestling at the time if you want to count MMA Sakuraba and Sapp x 2 are further for Japan) That's a 3 on 3 split in wrestling and two of those for the US were from a guy who spent the majority of the time in movies than wrestling. The US was dominant during the AE but now it's pretty damn close.