Given the circus that would be sure to surround him had he been included in the Oval squad, and the fact that Kerrigan is unlikely to play, it makes sense not to have included him now. There is simply too much going on for that to have been a viable option. And, looking to the future, there is a chance to see how Kerrigan, uncapped in any of the formats, fits into the group.
This does not, or should not anyway, give an indication about the winter, however. If Graeme Swann were unable to play in this coming Test, then, with the Ashes won, there would be nothing lost by playing Kerrigan.