> But they need not be functional or even intelligible as anything other than as part of instructions, e.g., short strings of octal values representing characters, with wildcard characters interspersed.

I think you're misunderstanding how copyright law views works. A "work" in the sense of copyright law isn't a pattern of bits: it's a creative expression of an idea (a binding between a pattern of bits and some concept in a human brain) that has a context for how it came to exist.

The classic article "What Colour are your bits" is a good overview of this: http://ansuz.sooke.bc.ca/entry/23

It's worth reading, to understand exactly what copyright law covers / how it works. But suffice it to say that the ability to create a set of bits that does not include any inherent reference to the GPL'd work does not make the bits no longer a derivative work, any more than Monolith (the example from that article) causes bits to stop being copyrighted.

Which answers your question of why programmers do not distribute instructions on how to modify GPL source code without distributing the source itself: there's no point. The legal requirements on them are exactly the same.

My comment about BSD licensing is that if people who own GPL'd works sometimes accept payment to give you the work without the requirements of the GPL, nothing is stopping people who own BSD-licensed works to accept payment to give you the work without the requirements of the BSD license. If it's a bad thing that you can in theory pay money to avoid the GPL, it's equally a bad thing that you can in theory pay money to avoid the BSD license.