You don't need to win the Pac. You used to have to win the Pac, but you don't anymore.
When a bowl game is easier to get into, it's less than what it was.
It's still a big game, and it still was a very good win for us, but all of the nostalgia and prestige that makes the Rosebowl such a big game was built up during a period in which UW, not USC, would have played in it, because they earned the larger prize.
Nobody would have passed on the Rose bowl in the past. There was no greater game. UW did. Because there was a bigger game for them. The rosebowl you remember doesn't exist anymore. What we have is a step down. Which is why USC was able to play in it.