"See the delay? You need that, because otherwise when you try to move your mouse from the main menu to the submenu, the submenu will disappear out from under you like some sort of sick, unwinnable game of whack-a-mole."
How will a delay before displaying the submenu prevent that? If it would be a delay before it disappears I would understand but in the example it doesn't seem to have that.
If your submenu is extending from a link in the middle of the parent list, you don't want the current submenu to disappear if your mouse tracks across the corner of the link above or below the intended.
Consider this:
The link A | A sublink of B
Some Link B --> | Another sublink of B
A link C | And again a sublink of B
| Jez, B has a lot of sublinks
If the user mouses over "Some Link B" and the submenu expands, without a delay (or other mechanism such as the triangle effect described in the article) the submenu could disappear when the user tries to move from "Some Link B" to "Jez, B has a lot of sublinks" if it happened to cross the plane into "A link C" or out of the navigation list entirely.
How will a delay before displaying the submenu prevent that? If it would be a delay before it disappears I would understand but in the example it doesn't seem to have that.