From Google's help page: "The significance of each keyword reflects how often it's found on your site's pages. Click each keyword to see a sampling of pages on which it appears. Both keywords and their variants are listed in order of frequency of appearance."
It's interesting that words like "for" and "sale" should be considered "key". Although I've seen "VAT" (as in the British tax) appear before on the Content Keywords section of a UK e-commerce site.
My guess is they've stripped out ubiquitous words from the report as a separate upgrade to make that section of WMT more useful and your drop in ranking is coincidental.