I've always loved this little detail. A bit of trivia about the spot:
This stream passes under a short span of wooden walkway, and is visible on both sides of the path. It marks the border of Liberty Square and Frontierland. It represents the Mississippi River, as you pass over it you are entering (or leaving, I guess) the "wild west."
You are right, thousands of people pass right by the spot and never notice it. Makes me wonder how many other awesome spaces there are at WDW that I pass by.