To be honest it makes no sense to me. Whether he's bowling better or worse than before his elbow op early in the year, there's no doubt he deserved to be on the tour. The vast majority of observers would still have him down as the best spinner in England, even before considering his catching at 2nd slip and his batting down the order. None of that has changed in the course of 3 matches.
In those 3 matches Swann's figures have been very poor, but there's always the little nuances to consider. Swann's wickets have been the top order batsmen or Mitchell Johnson (Clarke x 3, Warner x 2, Rogers, Bailey, Johnson). And unfortunately his team mates haven't helped him out - Root dropped Clarke when he was on 18 in the first innings at Adelaide before he went on to score a hundred, and Prior sadly missed two opportunities to stump Warner in the 2nd innings at Perth. So things aren't quite as bad as the numbers suggest given that one of the world's best players of spin has succumbed 3 times and also been dropped of Swann's bowling.
That's not to say that he should necessarily have been picked for the MCG - his place quite rightly was in question. It's possible he would have been dropped, but that was the case for a number of England players. They all took the decision to be part of the Ashes squad and unless they are medically unfit to play (i.e. Trott), they should be there for the duration. It's obvious that retiring mid-tour will have huge pick up in the press and completely destabilise the side. So I can't work out Swann's decision - it can be described as selfish, the actions of a quitter, gutless, etc.
Interesting then to see that his decision has been defended by the likes of Vaughan and Boycott. Vaughan says that he's not being selfish because he's given up 9 months money rather than seeing out his contract. And Boycott says that's "it takes a brave man" to do what he has done. What a load of b***sh*t! He's a rich man anyway and doesn't need the money as he'll walk into another highly paid line of work. What would be fair to say is that if, as David Lloyd says in the same piece, Swann is all about the team, then he's made a big mistake. Mistakes are part and parcel of life, and can be forgiven, but to try and pass off a mid-tour retirement as anything other than entirely detrimental to the team is lunacy.
I heard Jonathan Agnew giving an interview in which he suggested that the management team had given Swann the nod that he would be dropped and therefore given him the opportunity to retire first. I wouldn't rule that out, but if Swann was as much of a team man as everyone says he is, then the response would have been to continue and to support Panesar and the rest of the side by helping them prepare for the MCG. Not cause a commotion, tell the press that you'd like to see Scott Borthwick selected (which is really going to help Panesar as he prepares for the Boxing Day Test) or say anything that could be twisted by the media to be a criticism of his ex-England team mates.
Frustrating really - such a great player for England but he's not handled the retirement process at all well. England need to learn from this - before Clive Woodward took the 2003 World Cup winning rugby team to Australia they discussed the retirement issue as a number of players were at the end of their careers. They agreed as a team not to announce retirements, or discuss them, until after the tournament. How Flower must be wishing he'd had the same foresight to agree the handling of retirements pre-tour as Woodward did.