The problem with judging this is confirmation bias, though. I only notice it when google has infuriatingly dropped the key term in my query, but I search for things at least ten or twenty more times each day. Google may be doing the same thing there and I just don't notice, and it's actually helpful.

I wonder if it would help if they added some heuristic where, especially if it looks like a technical topic, it would try to find the word that was most domain-defining (in your example: "ruby") and never drop that one. I wonder how difficult that would be to solve. Even with a lot of false positives, the worst that you'd get is the results quality of not dropping any of the terms.