Defence of the GPL realm (The H)

It means that if you have the source code for the firmware for a network card, or a hard drive, you don't have to be given the compiler. After all, it is a normally distributed part of the operating system on which the executable runs: in that case, the chip hardware. And to get that special compiler or even the opcode list for the processor might require committing to the purchase of a very expensive dev kit. If the ASIC is completely custom and proprietary you might not be able to get a compiler at all.