Except there are lots of other "power user" things that are built in. Where do you draw the line?

It's more likely that they just consider package management out of scope for their part of development-- something that benefits too few people to be worth the cost. Seems to have paid off, too-- package management has been well-handled on OSX for a long time, both through semi-sanctioned projects like MacPorts (which is community-developed but is hosted by Apple) and through community projects like Fink and Homebrew.