I do the same as you, but was just thinking that if most users search using full sentences then Google will spend most effort optimizing for that, so maybe we're the ones getting the worse results?
No, the optimization they do for the low-quality query is more than balanced out by the higher clarity and relevance of a well-phrased query. There are often extraneous words that aren't simple stop words, and they're not 100% successful at removing these extraneous ones.