Vladek is strictly speaking - correct. Some people get asked about their ability to support themselves and some don't. I imagine that depends on a number of factors (location of embassy/education/experience of candidate/self assurance and appearance of candidate/mood of the CO/lots of other things).
If they ask for proof of your ability to support yourself and you have nothing in hand, they could deny you immediately or they might put you on AP while you get some evidence to prove that you can support yourself. That happened to one of the board members in DV2014 already.
However, passing the interview is one thing, but in order to move to the USA you WILL need money - how will you support yourself - what is your plan. Perhaps you have a good plan and can show it to the CO or perhaps you have no idea in which case you probably should think twice about going.