Mac question: how to search in open folder in the finder by default?

On my MacBook Air, if I want to search inside a specific folder in the finder window, such as “iTunes”, when I type something in the search bar in the upper right-hand corner of the computer, it will search “iTunes” or whatever folder I am in automatically.

However, on my brother’s MacBook, if you are in the “iTunes” folder, for example, and type in something in the search bar, it will automatically search the entire computer rather than just the folder. How come it searches the open folder by default on my computer and the entire computer by default on my brother’s computer?

Both are running the latest fully-updated versions of Mac OS X Lion.