3D Software and Realistic World are same indeed, because according to Modern physics the realistic world is nothing more than an illusion. Most of the Western Philosophers and Scientists including Einstein the Great believe that our realistic world is nothing but just an illusion.
We believe that we exist however it’s not totally true, because whatsoever we observe is just perception or conception of our five senses. Even the Father of Modern Western Descartes says, “I think so I am” otherwise nothing is to make my belief that I exist in this world. Anyhow we are not studying philosophy here, we are just trying to understand the difference between realistic world and any of 3D Software such as Maya, 3D Studio max, AutoCAD or somewhat else. When we work within Maya, actually we use a 2 Dimension Screen of our LCD or Monitor as drawing canvas. So the difference between realistic world and 3D software is clear that we just model or animate 2 dimensional entities on an imaginary 3 dimensional canvas. It’s just like drawing an apple on a paper with shades that make apple’s round rather we model things in our realistic world on a realistic canvas which is our space, our surroundings, our environment.