I think its because traditionally he's been able to mould players to fit into his systems. Turning Henry & Van Persie into CF's, Kolo Toure into a CB, Song into a DM etc.. In order to accomodate Arshavin as a second striker we would have had to change formation - which would have ment dropping a midfielder.
I am just annoyed by cliches. Arshavin is always "diminutive", but I have never ever heard of a diminutive Scholes or Tevez, who are actually shorter.
Arshavin was very lazy and lethargic in the 1st half. Him and Walcott (1st half) were awful. Arshavin gave the ball away on numerous occasions. 2nd half though, both were superb. Miguel was outstanding, as was Coq. Even Cham looked very good and worked very hard when he came on.