2. The AF system is great—no, make that GREAT! However, not all lenses of a particular maximum aperture work the same. In other words, some f/4 lenses will be able to use more of the focus points than others. Put another way, some focus points may be "cross-type" with some f/4 lenses but not with others. What lenses work with particular focusing points is spelled out in the manual but there's no explanation as to why. I'd love to know. It doesn't seem related to the release date of the lens.
It has to do with the location of the exit pupil of the lens.
AF units have angular sensitivity. An f/2.8 focusing sensor has a spread of 20 degrees, meaning one line looks at one side of the exit pupil (the circle that is the virtual aperture, as you look at the back of the lens) and the other looks at the other side, and there's a 20 degree difference. For f/5.6 sensors, it's 10 degree.
Now with a lens such as a macro lens, the exit pupil can be much further up in the lens, as you focus closer and closer. So even if it's ostensibly an "f2.8" lens, since the exit pupil is so far away, it's outside the angle of view of the f/2.8 sensors.
If you look up "bellows factor," you'll see that at a magnification of 1:1, lenses lose two stops of aperture. So an f/2.8 lens is really f/5.6, at 1:1.
There are other lenses that lose AF points for similar reasons. The legendary 1200mm f/5.6L can only use the central cluster of AF points, for instance. As can be easily visualized, the exit pupil is probably pretty far up the lens barrel, making it invisible to the AF points that aren't near the center.
Really, it's all about geometry.