You've lost me.
The categories are based on Vat. End of story. If 1.3Vs (ie Vat) in the 737 is greater than 140kts at MLW (as per the Flight Manual), then it's Cat D. If 1.3Vs is 140 or less, it's Cat C. As far as I can see, it's got nothing to do with Approach speed. If I chucked on +15 for wind, do I then have to brief a Cat D approach? Your chart shows you can be doing 160KIAS quite happily as a Cat C, so it cannot be based on "Approach Speed" being 140 or less for Cat C. It's based on Vat/13.Vs only.