Have you ever played a game of Scrabble against someone with a limited vocabulary? Like the time that I played against a couple friends and laid out the word rapt. Not exactly a high-scoring word, now is it? Nonetheless, the girl pointed out that rapt wasn't a word. I assured her that it is a word. She declined my offered definition.
She then asked me the ultimate Scrabble-challenge question: use rapt in a sentence. By this time, I was fairly flustered and the best I could come up with was: Rapt is a word. It's a complete sentence, grammatically sound, and it is also a true sentence. Alas, I only won after the fun of the game was thoroughly ground into the dirt.
My feelings when playing Bookworm are similarly unpleasant. Here, not only are you unable to use some words for mysterious reasons, but you also cannot argue that you're right. Case in point: look at the image above. Wizened is a word, as surely as rapt is and rofl isn't.
I raged against my machine that day, I'll tell you. The feeling of such bitter and ignominious defeat, of plummeting from the lexical heights of Bookwormdom's noble court (the 7-letter+ word club)... it soured my whole Bookworming experience and I have not played since.
Then you play Scrabulous on Facebook and somehow za is a word. The vocabulary world has turned against me.