With EE unemployment so low, I think you'll see that changing. Nonetheless, it's incumbent on you to let the employer know from the start if you will require help with your relocation. To drop this on them just before, or right after, they make an offer isn't going to put you in a good light. Some people might argue that you'll get leverage in your negotiations if you let the deal proceed to the offer, then bring up the relo issue. Here is the real issue as I see it.
Few things are black and white.
There's usually some negotiating room, if you step forward and try to develop it. Sta rt by asking them how they handle relocations before you interview. That may satisfy you. If you want to work with them, make sure you already have a collection of options in mind. Let them know that you'd like to work out a deal that will get you the help you need and that will also be acceptable to them.