I also thought that they would be similar. However, I spoke with another designer and, without going into detail, there seemed to be noticeable differences between the two. I don't know how old their guide was.
My issue with the color guide (coated) is that I have a match in incandescent lighting and another in daylight. I suppose that Pantones are sampled in neutral light. From what I can see, the coated paper is more reactive to red light. I expect the plastic chips to behave more like keycaps.
Taking a spectrometer to keycaps and Pantone plastic chips would indeed be interesting and quite useful for rendering.