All of these spaces are defined as LATEX commands to overcome limitations in length evaluation. For example, if LeftMarginSBVerse were to be defined as a length and then immediately set to 4em's, the specific length would be evaluated with respect to the current font. This may not be what is desired; instead a length evaluated with respect to the font in place at the start of an SBVerse is probably what is desired. This can only be done by making these lengths LATEX commands (as far as I know).