An ipython interpreter has certain nice-to-use features that provide more ease of use. It has syntax highlighting, file navigation/system commands that can be easily run inside the console, magic commands like %edit to access special features, tab completion etc.
All of these features make it easy and faster to use.
The main difference is that IPython is IPython notebook. You can put all your work into a notebook like script, image files, etc. But with normal python interpreter, you can only make the script in a file and execute it.