Windrose and latitude lines difference

Looking at several charts, especially some in chart books, I noticed that there can be a considerable difference between north shown by latitude lines and north shown on the wind rose. As a rule I would use the True bearing shown on the wind rose but my plotter instructions Portland Course Plotter) tells me to use the nearest latitude or longitude line that in some charts are off by over 1 degree. Aren't latitude lines all converging on True North? I realize that perfection is an utopia in navigation but nevertheless I would like some expert practical advice.