First off, do you have some source that denotes eladrin as being an elf? From what I've gathered, the eladrin were specifically conceived as not being elves, but rather displacing the elf' as the ephemeral, immaculate, sophisticated, somewhat-anemic masters of magic. The elves will be the earthy tree-lovers wearing animal skins and weaving dirty sticks into their hair. You asked what's the point. That's it. It resolves the elven identity crisis.
Now, some folks might feel tempted to respond that if eladrin wind up being thin and pointy-eared, then they're elves as far you're concerned, but all that response does is point out how meaningless it is to make a distinction whether or not a race is elven, because all it amounts to being thin and pointy-eared. Let halflings be an elven subrace for all its worth.
Drow have always had lots of things that made them distinct from other elves, both physically and in a mechanical sense.
Half-elves I admittedly just don't get. Never have. It seems that in 4e, they willl be the leaders and face-men.