Strikers are those who are meant to score goals. So they are judged by their goalscoring (or goal creating) ability. Midfielders are supposed to create goals and do other things like keep possession. They are judged on that. Defenders are supposed to hold the fort. They are judged on that.
So if you're asking me "would you be so radical as to judge a defender on a single mistake he made during the match, the same way you judge a striker on a single goal he scored", the answer is yes. Except defenders have more of those crucial moments in a match than do strikers. A striker gets maybe 5 chances per match. If he doesn't take one of them, he's not doing his job. Not every single match, of course, but on a fairly regular basis.
Assists count, I already said that. Anything counts that contributes directly to a goal being scored by whomever. But "pressing" or "possession" for its own sake is not something you deserve a medal for, not when you're a striker.
Defenders score too Martin, along with midfielders. and vise verse, attackers also help the defense, just like we saw Crespo a lot helping his defense. Football is not that simple, defenders to defend and attackers to attack
only.
I prefer Iaquinta over Trezeguet , because Iaquinta does his job everywhere, he scores, creates, defends, for this reason I rate him higher that Trezeguet. Sure he has to score also. But scoring is not everything like I said. For example, when Trezeguet is off form, the team play like 10 players, which makes the team much weaker, for this exact reason I prefer Amauri over him, because Amauri helps the midfield too unlike Trezeguet. If it was up to me I would bench both and play Iaquinta and Del Piero up front.
We saw when Trezeguet played that full match, he wasted loads of chacnes, and we were like playing with 10 men, how about that? If Trezeguet goes back to his old form, and starts scoring loads of goals, I wouldn't mind of having him play. But, he is not in that form yet, I would play him in small games, but would not risk in a big match like Bayern's. Yes I know he scored two (lucky) goals, which the rate statistically makes him one of the best striker in the world at the moment, when you and I know that he isn't al that right now.