Why do people say that liberals think money grows on trees?

An anecdote from the Rush Limbaugh show:

RUSH: This is Pam in Cincinnati.  Hi, Pam.  Great to have you on the Rush Limbaugh program.  Hello.
CALLER:  Hi, Rush.  Thanks for taking my call.
RUSH:  You bet.
CALLER:  I am a self-employed hairdresser, salon owner in Cincinnati. I've been self-employed for about 14 years.  Just after the 2008 elections, I had a client come in to the salon and she was born and raised in Italy and said that she had come to the United States in 1990s and how she loved the United States and that she was self-employed here, and I asked her, "Well, can you not be self-employed in Italy?" And she said, "Oh, no. No one is self-employed in Europe because the taxes are so high."  She had quickly become an American citizen.  Well, I asked her, "How do you like Barack Obama and all that he's doing?"  She said, "Well, I love Barack Obama.  I'm very, very liberal," and I knew right then that she truly did not understand how capitalism worked, because she didn't understand where the money came from.