The speed of light is VARIABLE and Einsteinians do extract profit from this fact but "without wrecking the whole thing too much" (we all live in Einstein's schizophrenic world, don't we):
http://arxiv.org/PS_cache/astro-ph/p.../0305457v3.pdf
Joao Magueijo: "In sharp contrast, the constancy of the speed of light has remain sacred, and the term "heresy" is occasionally used in relation to "varying speed of light theories". The reason is clear: the constancy of c, unlike the constancy of G or e, is the pillar of special relativity and thus of modern physics. Varying c theories are expected to cause much more structural damage to physics formalism than other varying constant theories."
http://www.telegraph.co.uk/technolog...ht-discovered/
"But the researchers said they spent a lot of time working on a theory that wouldn't destabilise our understanding of physics. "The whole of physics is predicated on the constancy of the speed of light," Joao Magueijo told Motherboard. "So we had to find ways to change the speed of light without wrecking the whole thing too much."
Pentcho Valev