Xcode 3 doesn't solve the issue of it being a real pain in the butt to install. gcc by itself is much, much smaller and much less of an issue for a casual user to install.
A casual developer might be a different class of user ... but anyone who hits the point of writing code & installing libraries instead of applications has adequately stepped outside the role of user.
And even granting that, it is still not a firm enough basis on which to argue such an inflammatory statement as "OS X is not for developers"--when the casual developer is far better served by OS X's included toolchain than s/he is going to find in a default installation of Windows/Linux counterparts.
OS X is not "for" developers when it begins removing the tools that create the lowest barrier to entry for casual development I've seen in a default OS installation in the last 10 years (except maybe Gentoo Linux, one of the most "for developers" systems I've had the pleasure of using).
I think that's the main argument. Getting started with command-line tools and developer-type stuff should be as easy as possible, so that people can try new things and break stereotypes and do more than they thought they could do.
I agree that a smaller (and free) tool chain would be great, but so far as I know there is nothing preventing anyone from making one.
Related, I realize it is now the case, but when did casual users start needing gcc? Time was, in my pre-OSX days, compiling things yourself if you weren't a dev was seen as somewhat pointless, you just get thousands of users all building the same binary instead of building one binary to be downloaded by thousands of users...
But, your point was about developers. When did casual users come into the discussion?
But I still have difficulty believing these casual-developers-but-not-programmers exist in great numbers. Have people told you "I was going to try your thing, but it asked for this weird gcc thing"?