He is a scorer of great goals, not a great scorer of goals.
I don't rate, and never rated Iaquinta. I don't care how many awesome goals a player scores. It's how crucial or important these goals are. Cavani and Falcao don't always score great goals, but they can be relied upon to come good when need be. The came can't said be for Quag and Iaquinta. Del Piero is obviously on a whole different level, and an exceptionally talented footballer.
I disagree regarding Vucinic. Gio is still young, and the comparison is somewhat unfair. Regarding Matri and Bendtner, it's fair to say that they aren't exactly world beaters, and Quag should definitely be ahead of them in the pecking order. However, him being our first option of the bench is testament to how poor our attack is, more than a true barometer of Quag's ability.