You have to assume there is some motivation of $$$$, I am surprised he decided to axe ODIs though as he's been a member of the no 1 ranked Test side, of the T20 World Cup winners yet hasn't even reached a 50 over World Cup final.
And of course assuming he will stick with IPL and other money spinning T20 tournaments, surely the shorter format would tie in better?
Pietersen
85 Tests, 6779 runs @ 49.12 (SR 62.80, 100 x20)
127 ODIs, 4184 runs @ 41.84 (SR 86.75, 100 x9)
36 T20Is, 1176 runs @ 37.94 (SR 141.52, 100 x0)
Do I buy into the age reason, letting younger players prepare for the next World Cup? Not really, unless he intended retiring sometime time closer to, but still before, the World Cup which I doubt. Maybe he's just backing up his philosophy with actions, but surely England should decide what policies they employ?
In some ways I think England would be better off without him, like the football team without Beckham and arguably even Liverpool without Gerrard.