alt Hacker NewsSuper fun, got 70,250. Friends have always lightly ribbed me for having to go home and look up words i've used. Those remaining 100k words must be really obscure.
One suggestion would be more convincing decoy choices, some were pretty silly. But I have no idea how they come up with them.
Open any technical textbook in an area slightly outside your domain and you will quickly disabuse yourself of the notion that majority of words are obscure. Most complex words are just technical/jargon not archaic or forgotten.