Wenger makes all of his young players do shifts either out wide, or deeper in midfield when they're still developing. Not until they're approaching their peaks do they get given the crucial #9 or #10 positions. Fabregas is an exception I think, as he was so advanced as a 16 year old.
Walcott should be playing as a striker imo.
He should now because they have no options. Not in the past though, he's too limited and they had better forwards. Wenger's been trying to improve his allround game by playing wide, unfortunately footballers are clearly too thick to realise the benefits, instead selfishly wanting to play 'thru da middle'.