There's a gulf between a stereotypical "day job" developer and someone for whom programming is a core part of their self image, but in real life there's more of a subtle gradient.
People who write technical blogs, go to user groups, or endlessly read programming books seem to be in the "not us" group, but I know of day job developers who do (some/all of) those things. Drawing lines in the sand doesn't seem useful when, I think, the issue behind this seems to be "don't look down on us day job developers." :-)
You're right (I'm probably in the gradient somewhere), but I don't think that bit of the manifesto is the crux. There are lots of people in many vocations who contribute to their field without given up massive amounts of their spare time. Some folks choose to give up their time, and, as the manifesto says, more power to them.
The bigger takeaway for me from the manifesto is the first half--that my job is my job. I enjoy my co-workers, but, truthfully, I enjoy my family and friends more. And that should be okay.
People who write technical blogs, go to user groups, or endlessly read programming books seem to be in the "not us" group, but I know of day job developers who do (some/all of) those things. Drawing lines in the sand doesn't seem useful when, I think, the issue behind this seems to be "don't look down on us day job developers." :-)