The few of points I've made about this are: 1. The Xcode 4 download compared to Xcode 3 is basically just a different IDE. The gcc version is, for all intents and purposes, identical. There's nothing stopping anybody from just installing that if all they need is the toolchain. 2. The other big 2 OS's (Windows and Ubuntu) don't have any build tools installed by default either. Granted they are just an apt-get away on…
If I wasn't a dev, I'd be pissed to find out some compiler toolchain IDE gongshow eating up 5-15GB of my disk space Yeah, but the essentials that most command line builds require wouldn't even take up 10% of that. Apple already wastes gigabytes on printer drivers and extra languages you don't need.
Since Snow Leopard, printer drivers are no longer included with the OS either. Instead, they are downloaded through Software Update as soon as you plug a printer in.
Having said that, the fact that Xcode is listed on the Mac App Store instead of just in the developer portal, I suspect that Apple will bundle Xcode 4 with Lion to try to encourage more app development.