That's an approximate number I used to let you know how special Jass is against GUI.
Now, let me tell you. Most of the systems are made in Jass or vJass.
So, Jass can display something to only one player, Jass can detect the left click of the mouse (a.k.a trackables), Jass can Remove the leaks (yes, that Custom script action is the intercessor of GUI and Jass, a way GUI can communicate with the Jass language), Jass can be more precise in some events, Jass can generate events, Jass can move Lightnings in the Z axis, Jass has certain "Get" functions that GUI hasn't, e.g. GetAbilityId(). There are thousdans of functions GUI can't even dream of; this is not the Jass's 'actual power', it's just the fact that some Jass functions haven't been implemented in the GUI.