The lines are now a little bit lighter in weight and no longer span the
full width of the list item; now they have margins equal to
which is used for the items inside the list item itself. This makes the
lones no longer so visually objectionable, which makes them suitable for
keeping as the default appearance in list views.
Also, the top separator is removed because it is unneeded; only having one separator at the bottom of each list item is visually sufficient, and fixed a preventing you from removing the separators inside a list item when it has a colored rectangle, since the bottom-most line is actually drawn by the item below it.
(You may need to open each image in a different tab and rapidly switch between them to notice the difference)
BUG: 428739 FIXED-IN: 5.77