"Echt" appears in the Web version of the NYT (at least right this minute) only twice, so I presume its appearance in the paper is pretty rare. Remember, this list is of the top 50 words looked up, so the more often a word appears in the paper, the greater the chance it will be looked up. I'm sure there's also a strong correlation with which articles are most read. If a word appears only in unpopular articles, then it wouldn't appear in the top 50 list, either, even if it appears often. I must say, I loved the appearance of "baldenfreude," though.
Dan