Yeah, Pietersen should be in more due to his perceived threat (that he can really win a match by himself), and lack of options, than anything else. Performance-wise, he really hasn't delivered in the last couple of years. I guess 2011 is an improvement though, averaging nearly 30. Kind of like Sehwag getting an extended run around 2004-06 in ODIs though he was crap in that format for long stretches.
Having said that, it might not be a bad idea for England to bite the bullet and give a promising young 'un like Buttler a run over him in these relatively meaningless ODI series. India benefited a lot by giving the likes of Kohli, Raina and Pathan a lot of international experience and match-play in the lead-up to the World Cup. If Yuvraj had not hit form, he could have been dropped. Pathan turned out to be poor in the course of the tournament so he was replaced by Raina. Having several options and healthy competition never hurts. Right now, it seems there is an over-reliance on Pietersen because even though he is out of form, he has to be carried as it seems guys like Bell, Trott etc. cannot really replace what he brings to the team when he is at his best.