The segregation actually isn't so bad the more I think about it -- people with tons of karma from questions about mundane windows sysadmin and inane adolescent theming shouldn't be running roughshod over people trying to figure out how to do something in gmail.
That's right. The segmentation is about making sure that each site has a critical mass of experts, and enough of a focus that said experts won't be annoyed by off-topic questions. (Of course it's debatable where the line should be.)
Joel and Jeff have said several times that "Google is the UI". So the segmentation doesn't hurt the "answer consumers", who'll come in through Google with little regard for which site is which, while benefiting the "producers", who do care.
