One of the differences is that the output of headers_install is provided by the kernel maintainer for the purpose of integration into C libraries. That's different than just repurposing something else.
Your thinly-veiled FUD accusation is unwarranted. If it's (according to you) trivial for Google to use the output of headers_install, and if they do that in the future, everything's fine from my point of view. I'd love to see exactly that happen, and the sooner, the better. So the easier it is for them to do it, the better. Still I believe this must be done.