But...thats kind of what elves and dwarves are. Short people and forest people, created for a specific property (LOTR), used in another highly successful heavily derivative property (D&D) and frequently used after that in other derivative works. I've played great fantasy games with all new races. I don't really like the world-building aspect of having elves and dwarves if this game doesn't tie into the D&D cosmology. Which it might, we'll see I guess
In Dark Sun, elves are feasome desert-living marauders that kill and steal without remorse, halflings are jungle dwelling cannibals and dwarves are completly hairless and stoic to zen-like levels.
Now, it's a D&D setting, but it could just as well not be. All of the above is cool because these creatures are called elves, dwarves and halflings, because you understand they are invoking a certain image and then playing with it (in Dark Sun's case, it's what would've happened if a regular D&D world would have turned into a hell on earth.)
Just like in Shadowrun the mere presence of these creatures is cool and interesting because of the modern day setting.
I don't know how Obsidian is planning to use these races, and even if on the grand scale the race remain unchanged (elves are forest guys and dwarves are caves guys) maybe they're doing it to do something interesting with specific character - Like in BG2, where they used the character race and what you expect of it to great length (Mazzy is the most straight forward example.)
By using played and worn races and elements, they have more information in your mind to play with.