I don't have stats I can share, but I assure you that this problem has confounded many interview candidates with strong resumes. I agree with you that it's all basic material -- that's deliberate. I'm glad you think it's too easy. :-)
When applicants prepare for an interview, they do not often know what kind of knowledge to load in their heads. For example, just a couple of weeks ago I was asked to figure out a simple bit-flipping scheme, and bit string manipulations are something that I have not thought about in many years. So it took me about 10 minutes for a problem that I would have done in less than a minute when I was spending time thinking about similar things and my mind was full with them.
Being prepared for a technical interview does not mean to have memorized a few solutions to a few problems, but it means to have played with them sufficiently to have the brain loaded with the material. This helps with intuition as well as specific technical skills.