This has nothing to do with the OS you're using. It's the way the
input() function behaves.
When you enter a word without quotes, the python interpreter (via the input() function) is looking for a variable. Look at the following code:
foo = "bar"
sometext = input("Add some text here: ")
print(sometext)
Now run this code and enter
foo without quotes.
Add some text here: foo
bar
What happened was that python looked for a variable called foo, found it and displayed its value ("bar").
There are ways to circumvent this and present a more "user-friendly" approach. It depends on the Python version you are using, and may be a bit more complicated to set up than input.
You can take a look at 'raw_input' or the 'cmd' module.