IMHO author is missing the point here, lines are not just arbitrary decoration, they've got an important purpose to guide the eye. If line is removed, it needs

IMHO author is missing the point here, lines are not just arbitrary decoration, they've got an important purpose to guide the eye. If line is removed, it needs to be replaced by enough white space that will separate the content visually. The 1st example fails horribly with this, it's impossible to see where the 2nd row begins without reading the whole text. Also, the longer a row/column is, harder it is to follow the separation and line is a better choice in those cases (or more spacing is needed). There's nothing particularly special about these "rules", they're just the normal typography practices and some common sense applied to tables.