Well, it's always been that way, since Civilization 1. Lincoln represented the Americans.
I think it is because Lincoln was more of the leader role. Lincoln not only was born as an authentic, rustic and slightly impovershed American (Washington was also born in America, I believe, but to a wealthy plantation-owning family in an affluent area of new england) but because he proved himself to be a dynamic leader and led a nation that was divided.
Washington was the general of the Continental Army. His presidency was fairly unremarkable other than being the first one. I mean really, what do you think of when you think of George Washington? He led a tattered, amateur army against an overwhelmingly superior British Army, and after several initial setbacks, succeeded brilliantly. But do you remember anything he did as president? This is not to take anything away from our founding father, I'm sure that building a new nation out of a throwaway resource colony was quite a feat. But I think Lincoln was more of an all-around leader, not a military one.
Also, I was noticing your quote in your sig. One of my favorite movie quotes was Hans Gruber in Die Hard quoting "When Alexander saw the breadth of his domain, he wept, for there were no more worlds to conquer..."
Your quote looks much more authenic. I guess the movie misquoted... or glossed it over so Average Joe Moviegoer could get the gist...