and out of the handful of younger guys receiving regular playing time, the only one you could really say is performing below expectations is Cain. any additional pressure would be derived from the lack of talent/confidence in the everyday lineup, moreso than their relative youth or inexperience
so i would agree that the players know that this is not a good offense and that has to be in the back of their mind somewhere- though i think that is a bigger factor with someone like Cain, who has pitched very well at times without getting rewarded with wins and may be putting too much pressure on himself to be perfect.
i think Zito's struggles are a combination of the pressure to justify the ridiculous contract and gradually diminishing skills- which have snowballed this year into the trainwreck that we have witnessed over the first half of the season.