wenger knows how good diaby is so thats why he keeps him..
balotelli is a good player on his day, but no one knows when that day will be. thats why he isnt worth the risk. giroud for instance might average 10 goals a season, balotelli might get 20 in one, then 2 in the other. he isnt worht it.
mancini might be keeping him, but htere is a differnce between keeping him and not playing him