I take it there isn't exactly a coincidence between you finding my question regarding geostationary orbits and you asking this question about Hill Spheres? :-)
The chart you found does seem counter-intuitive at first. But consider this chart:
(I wish I could add it here, but I can't manage to add it as an image, just as a link).
There's another pattern, and it has to do with distances from the Sun, and from nearby bodies. As you go out into the outer solar system, planets start to get farther apart. For example, Uranus is twice as far away as Saturn, separated by 10 AU at their closest, and Neptune is, at the closest position to Neptune, 10 AU away. That means that each planet is separated by a large margin from other planets, and Uranus and Neptune have virtually nothing else to contend with in the outer solar system, because they are so far away from any other massive bodies that could take over (i.e. Jupiter and/or Saturn).
Pluto, Ceres, and Eris are interesting cases. As far as I can tell, they have large Hill spheres because they are the largest of a collection of similar bodies. Ceres dominates the asteroid belt, and Pluto is so big it was once (in what now seems like ancient times) considered to be a planet. Eris, too, is quite large.
The only anomaly here is, actually, Pluto - and that's only for a [relatively] short portion of a time. It comes closer towards the Sun than Neptune for a portion of its orbit, which would seem to indicate that Neptune shortens Pluto's Hill sphere, but in reality, the two are rarely near where their orbits intersect at the same time.