I don't think anyone is trying to say that psychology doesn't deal with statistics on some level. This is how we know things like that children of an abusive parent are more likely to be abusive themselves. This is valuable information to have, but what psychologists and psychiatriasts primarily do is help people through interpretive practice. They don't just throw their clients an equation and say "You're all better now". They do much more than that, they talk to people, build rapport, establish a relationship with them and use a variety of techniques drawing from various psychological theories to help them help themselves. These are great skills to have and psychologists/psychiatrists should be proud of what they do, but I just don't think it should be considered a science.
The example in my previous post may have been of a bad practitioner, but the way I see it, a good practitioner would still be using all those skills that I've mentioned and more to help people, but it's difficult to quantify to what extent that these people are being helped. If a psychologist sees someone about their anger and violence issues, the client may come away saying "Yes, I'm all fixed now" and the psychologist may provide his professional opinion and say "Yes, he's reformed. He'll never beat his wife again" but that's objective information. You don't know that he won't and that he doesn't harbour the desire to. It's not like a doctor curing someone of an illness or a chemist getting the right percentage of the active ingredient of a drug into a pill. This is what I meant in saying that behaviour is unmeasurable.
Social workers in direct practice draw from psychological theories when they work with clients too. There are almost no social work-exclusive theories out there. Social workers in research fields use the same kinds of methods to get their findings (surveys, questionnaires, longitudinal case studies) as those in psychology. Generally speaking, we have the skills as psychologists but with a focus on interpersonal relationships instead of intrapersonal. Yet I'm sure if someone stood up and proclaimed social work a science, they'd get laughed off the face of the planet.