Paladins in D2 also have Auras. It was more a universal theme of "Blizzard Paladins". In any case, the "theme" of Paladins is that they are leaders, inspiring their allies to overcome odds, and Auras were the in-game reflection of that. They were always the "subpar character that is amazing in a group", and while many players didn't like that style, it was certainly unique.
Blizzard really got carried away with homogenizing everyone, and I'm not entirely convinced they've learned their lesson, but hopefully they'll consider re-implementing unique Class mechanics again. Personally, I think "Holy Power" has been kind of a wash, though I respect them for trying something new, and the concept is certainly nice; I think Pallies are just in a very rough place right now.
Well, they will still have a minor glyph that makes their pony glow.
Auras and Paladins aren't really synonymous in Warcraft though. Maybe it was in D2, but Auras were hero-wide in Warcraft 3. Trueshot, Thorns, Endurance, Unholy, Brilliance... If there were anything I missed it was that element of providing buffs for allies. I thought they would have done that more with different classes/specs in Warcraft. It would've been nice to have a Frost Mage bring in a Cooldown reduction aura, while Fire brings in a Spell Crit aura. But with homogenization, who really cares about being a special snowflake any more.
They're going in the opposite direction I want them to go, but at least the game's balanced :/