Leaving aside the truth of what you write -- can one person's electoral campaign really be the source of such an apolitical turn? -- I find it interesting that the argument you marshal here is precisely the opposite of what many people on the left -- including, since I'm typing to this list, our esteemed moderator and host -- argued four years ago. Which is to say, in 2004, Kerry's election would allow for some breathing room, give the left the space and desire to really push for progressive change, etc. In 2008, things look very different. Whereas a Kerry presidency would (negatively) inspire, or at least allow for, "genuine left/progressive politics," an Obama presidency, the consensus seems to go, would ensure its "neutralization."
What's changed, I wonder, in four years?