Allow whitespace before the commas?

For a group of selectors the grammar (although not the prose which seems to disallow any whitespace; an interpretation promptly refuted by the example) in the Selectors WD allows whitespace after a comma separating selectors but not before. Is there a particular important reason for this? If not, I suggest this restriction be lifted as it creates a likely pitfall for authors. (I feel the prose needn't be amended though.)