I'm not saying that borders are always wrong, but you are using a horrible example as an argument in favor of borders.
There are no borders in any of the examples in Josef Müller-Brockmann's Grid Systems except for in the pictographic signs used by the the Swiss Federal Railwaws, but they are not part of a grid.
Well, there are also borders, or rather literal guidelines, in all the sketches visualizing the grid, but they are of course only there as a tool. In all the grid layout examples the grid is implicit. All of them.
I am pretty sure the complaint above was about keyboard navigation, i.e. the possibility to navigate a page and its components with the tab, enter, space and arrow keys.
There are no borders in any of the examples in Josef Müller-Brockmann's Grid Systems except for in the pictographic signs used by the the Swiss Federal Railwaws, but they are not part of a grid.
Well, there are also borders, or rather literal guidelines, in all the sketches visualizing the grid, but they are of course only there as a tool. In all the grid layout examples the grid is implicit. All of them.