This doubles as a little thing I like, as its a cool pattern right until the end when something bungles it up.
So the Eeveelutions all come in sets, and within each set, their abilities follow different themes.
The primary abilities of the Kanto trio all grant them an immunity to their respective types, and their hidden abilities all pertain to status effects in some way.
Both the primary and hidden abilities of the Sinnoh duo are weather-based abilities.
Sylveon's off doing its own thing, it doesn't have any counterparts.
And then we get to the Johto duo. Their primary abilities are the exact same ability
(kinda boring) and their hidden abilities have absolutely nothing to do with each other. I can excuse the identical primary abilities since it was Gen 3 and there weren't really that many abilities to choose from and they were still figuring things out, but come Gen 5, why did the devs give the Kanto and Sinnoh groups coherent themes for their hidden abilities, but then just not bother with the Johto duo?