There is quite a bit of value in winning, even in the preseason.
First, it can create a winning culture for all the players, on which the regular season can build.
Second, not only are the players trying to put their best on the field, so are the coaches (within scheme limitations). They still want to win, and I bet PC asks them to work toward winning.
Third, players learn how to win graciously, and what it takes to compete even against 2nd- and 3rd-string opponents.
Fourth, as was said above about those winning years with the LOB when we also won every preseason game, it became obvious that our depth was stronger than other teams' depths. That is probably correlated to winning.
Fifth, I'd rather see the Seahawks win a preseason game than my own local league team win. It's a much bigger stage, and the win matters more to my psyche. Maybe I'm shallow, but I enjoy winning. So there!