Developers, and power users in general, tend to like using the keyboard for moving around because it’s ofttimes faster to push a key or two than pick up the dominant hand, grab the mouse, click, then move the hand back to the keyboard.
The default behaviour on OS X is to skip drop-down (“list box”) controls when using the tab key to move around, which is at odds with using the keyboard for navigation. But, this can be changed in System Preferences.
