actually vitz and yaris is the same thing (only it will differ a bit in specifications in different countries). Vitz/Yaris is called Vitz in the Japanese market. and for other countries its called yaris, as u have found in the UAE.
and as for the other car u stated, the Holden Monaro is an Australian car, which is exported to the USA as a pontiac GTO and the middle east as a lumina SS. And they will differ a bit in specifications, specially made for that country, but basically its the same thing, only with different names.
wat i am always wondering is that y does the auto industry put different names of the same cars?? y cant they just put the car make and name as it is, so that car buyers wont get confused??