In addition to what openbear pointed out, it should be noted that the GPL requires build scripts to be included with the source. (What good would source do anybody without the three-bajillion-line Makefile that builds it?) GPLv3 also extends this to stuff needed to run the code on the hardware it's intended for (like tools to sign binaries so they'll run on locked-down embedded platforms like phones or DVRs).

There's a practical aspect to the GPL, here. The spirit of the license is, "if I can't view, modify, build, use, and redistribute the software, it's a violation."