Personally I would have taken AJ but it seems the decision not to is logical.
Regarding wingers Capello would have seen Lennon, SWP and Walcott, 2/3 of them were going to be in the squad, fast players, which lack creativity but are able to scare full backs with the pace and perhaps get in behind the defence and score or assist with a short pass.
Cole, Milner and Johnson, 2/3 were going. Milner was definate due to his season and England performances. Cole had the experience and the has more adaptability about him than Johnson, in the fact he can play behind the lone striker.
Personally I think Capello likes Johnson and if he was able to bring 24 players, it would have been him, not Walcott who got the nod. If I was England manager I would have made roughly the same decisions, apart from maybe Parker instead of Carrick, and brought Johnson as I would only have 7 defenders in the squad by excluding Upson. I think Fabio might have had this in mind when he persuaded Carragher out of retirement, but as he brought a demic in King it was difficult to do that.