Yes.
Doing a PhD isn't only about your technical skills and qualifications. It's hard work and success depends quite heavily on attitude. Interviews are a good way to assess how much the student wants the position because a student who gives up without finishing reflects very badly on the institute. Further, supervisors are looking to see if the student will get on well with other people in the lab and will fit into the culture of the place. They don't want to be wasting time breaking up fights!