While all of the lines may benefit from the practice you describe, I really don't think that's SS's prime motivation for stocking some higher end wines. Rather, I'm sure they stock them simply because some prefer them and will buy them. Even when the two of us are dining alone, I'd still prefer a really nice pinot with my duck + berry sauce rather than a mediocre one.
Based upon the list I've seen here, SS certainly charges less for their wines than their sister lines where you can expect 2.5X retail prices, so if you're correct that SS is trying to leverage some kind of "We buy, you buy" dynamic, they're certainly leaving a lot of $ on the table.