Some folks prefer the angled pickups as they say it delivers a more consistent tone across the strings. If you notice the ones with the horizontal pickups have the pole pieces spaced farther and farther away from the bridge as you go toward the bass strings.
I'm not entirely sure how much of a difference this makes, but my guess would be that they only offer active pups because they have not yet made slanted passive pickups.
Notice how with the slanted pickups the bobbins are staggered so that the pole pieces will line up properly with the strings. If you took a normal humbucker and did this, it would not be the case.