The layout list code seems to be set up so that a listitem can lose its ListRole if it's determined to be a layout list or presentational, but the <li> children retain their ListItemRole in all cases. This makes the DOM accessibility tree to have an ignored or generic group with listitem children. The main nav on Apple.com is currently an example of this.
Sorry. http://store.apple.com demos the issue. The Apple.com should probably count too though. They add role="navigation" to the list, which should override all the list semantics unless they were to use it on an element container ancestor of the list.
<rdar://problem/16360525>