Xcode’s distribution has changed greatly in 4.3.
First, it’s now simply an app, without an Installer package. If you install it through the Mac App Store, it’ll install directly–no more “Install Xcode.app” (which I think I read earlier that you have to delete, although I can’t speak to this myself). If you install it from the disk image, it’s a drag-and-drop install.
Second, the set of applications that come with it (now bundled inside) is now much smaller. The other developer applications have been split out into separate disk images that are only available on connect.apple.com.
So, I thought I’d make a catalog listing where everything is now. Every one of the below sections corresponds to a disk image on connect.apple.com, and with the exception of Xcode, every one of those disk images is only available from connect.apple.com—only Xcode is available from the Mac App Store.
I strongly suggest you bookmark Peter’s article, Xcode and Friends to keep track of the various developer applications that once came all together.
(Side note: Apple could have easily made them available as a developer bundle in the Developer section of the Mac App Store, anyway.)