Post by Ysera
Yes, they are different strands of the same race, but the class additions make sense.
The Splinterpost (I think that's correct) Trolls are the trolls you see dancing near Moonglade, the Druid haven. Trolls worship Loa (Animal Gods) Each tribe has it's own Loa and each have different ways to revere them.
Imagine, then, if the Splinterpost Trolls worshiped their Cat/Bear/Owlkin/Tree Elemental Gods by shapeshifting into them! Well, that'd mean they're druids, right? As to why they would worship those particulat Loa, they live very close to Moonglade, and northern Kalimdor is filled with those creatures. Much like other troll tribes, they worship animals native to their region (The Drakkari Trolls worship Mammoths and Bears, the Trolls of STV have raptor and tiger gods).
Now, when it comes to Night Elves being mages, that's a bit easier to explain. 10,000 years ago, far, far, before the squabbles of humans and orcs. The land part of Azeroth was one large continent and it was called Kalimdor. By large, I mean LARGE. Look at a map of Azeroth, see Kalimdor? See the Eastern Kingdoms? See Northrend and the Maelstrom? Well they were once all connected!
Kalimdor was huge! And in the center of it, where the Maelstrom is now, was the Well of Eternity. The Well of Eternity was a vast, magical, font' of power. Created by the Titans to fuel this peaceful world they had fashioned out of chaos. It drew it's power from the Great Dark Beyond. Well, the original Night Elves who were led by Queen Azshara, were adept at manipulating the power of the Well. They were arcane masters.
However, the demons found their little planet and convinced Azshara and her Night Elven nobility to open a portal, so they could come to take the power of the Well. Fortunately the first druid, Malfurion Stormrage, stopped the Highborne's plan. Unfortunately, the Well of Eternity, along with most of their continent, was destroyed.
At the moment, morale for Night Elven sorcery was at an all time low. Their font' of power was taken, so it was no longer the easy to use, fast results magic they had become accustomed to. Malfurion, the new leader of the Night Elves, had many taught the ways of Druidism. And, while it's nothing like the old magic, Druids still practice the arcane arts as Moonkin.
The Highborn were the nobles of Night Elven society. They lived within a walled palace in the capital city, Zin'Azshari. They last remnants of their society is found within Dire Maul. The Elves there still practice the old magics, they draw their power from the demon, Immol'thar. After the Sundering, Malfurion banished the Highborne. They left western Kalimdor and braved the waters of the new sea.
They arrived at the northern end of western Kalimdor (you may know western Kalimdor as the Eastern Kingdoms) and build a civilization there. They called their capital Silvermoon, as they were still predominantly creatures of the night (not vampires). Eventually they created the Sunwell. A new font' of power and took up the old magics again. These Highborne became the High Elves you know today. Who became the Blood Elves after Arthas ravaged their kingdom and defiled the Sunwell.
So, if Blizzard decided to add in Blood Elf druids, it couuuuuuuld make sense. But it'd be a bit wierd imo.
I would take this information with a healthy dose of speculation. I very well could be wrong. Also, I didn't bother looking up facts 'cause I was doing it quickly. Not to say that it isn't based on facts. It is. I may have missed a thing or two along the way, however.
Here are some links to Wowwiki, if you want to find out more about what I talked about.TrollsLoaNight ElvesWell of EternityWar of the AncientsShen'dralar
Mind you, a lot of this is guess work on my part. Based on what they've given us, and my knowledge of Warcraft lore.