There is a lot of misinformation in this thread. I'm going to try to clear a few things up based on what I've learned from talking to financial aid people at different interviews.
First, you are absolutely NOT required to fill out information pertaining to your parents. You are going to be a graduate student, and because of this will be treated as an independent student. However, filling out your parents' information CAN ONLY HELP you. You will get federal loans as long as you fill out a FAFSA with your information. However if you include your parent's info, schools will consider you for need-based aid. Most schools will not do so if you do not add your parent's information.
About EFC: I'm fairly sure that since graduate students are treated as independent, the EFC amount does not reflect your parent's income. Even if your parents make 500k/year, your EFC will still be low because it is based on your own income. Thus, many traditional applicants will have a low (nearly 0) EFC, but will not receive need based aid because their parents make a lot of money. People who have a > 0 EFC are likely people who work a lot, non-trads, or people who have a spouse that works a lot.