was Trezeguet a replacement for Inzaghi?
An improvement
Can you name a couple of SS's and a couple of Strikers?
I don't get what's your definition of those 2 positions.
Quagliarella is not a Striker. In my books, a Striker is a target man. A poacher who excels at positioning himself in the goal area so he can finish the move. A la Trezeguet, Van Nistelrooy (PSV, early Man Utd, Real Madrid), Gilardino, Inzaghi, ...
A SS on the other hand is a free roaming player who moves a lot between the midfield and the goal area, has good dribbling skills and can create an opportunity out of nowhere. Doesn't mean the player can't be a good poacher. It's just that he works a lot more during the match, creating a lot of movement. Examples of this being: Del Piero, Ibrahimovic, Aguero, Forlan, Villa, Dzeko, Rooney, Messi, Cassano, ...
I'd say Quagliarella fits this description.