> - General typographic convention is to measure vertical > motions in v's, not m's. CSTR #54's definitions of \u, \d, > and \r do not align with this common expectation.
I think this depends on what you consider the purpose of \d and \u to be. Obviously they are not needed: everything they do can be achieved with \v. However, if we assume they were intended as an easy way to get super- and subscripts (e.g., for footnote markers, or as in "H\d2\uO"), then you definitely want the motion to be in units of the current font size and not in baseline spacings. Otherwise, those super- and subscripts would be ripped from the text lines they belong to if you were to try setting the text double-spaced by requesting (say) .vs 24 for a 10-point font.
