I would like to argue that OP is correct, that indeed the value of Bitcoin DOES in fact relate to the value of energy (more specifically, useful free energy) that was used to create it.
In thermodynamics, the kind of energy that is important, for purposes of doing work, is not total energy but "free energy" - the energy that is available to do work. For example, a world consisting of a uniform hot bath of gas at thermal equilibrium could contain a lot of energy (heat energy), but none of this would be free energy - it cannot be used to do work. However, in a scenario where the exact same hot bath was coupled to a cold reservoir through a heat engine, part of the energy of the hot gas *would* be free energy and could be used to do work (the exact amount depends on the temperature and capacity of the cold reservoir).
This example illustrates that free energy (which really, is the only kind of energy that matters) does not inhere in a thing itself, it inheres in a *configuration* of things; most generally it could depend on the configuration of everything around it that might affect how much of the system's total energy can be usefully extracted as work.
In the modern world, a large part of what determines how much our environment can be extracted as useful work is the entire industrial economy, including the financial system. For example, if there were no mining machines, or no banks to fund the capital investment in mining machines, then (say) shale oil deep under the ocean would be inaccessible and would not constitute free energy for practical purposes. But, because our technologies and capital investment systems do exist, they can be used to extract that oil and use it to do useful work.
Thus, I would argue that money (like other elements of the infrastructure of modern civilization) indeed embodies (free) energy - since it enables the harnessing of energy - so its configuration in relation to other elements of our world is one that contains free energy, and likewise, free energy must be invested to produce any form of money that has value. Because, if a form of money can be produced without investing much energy in its production, then it will be overproduced, have a low market value, and be unable to cause much useful work to be done. The sad fact about the US dollar is that the only reason it still requires some amount of free energy (real effort) to produce is due to Fed policies (which aren't allowing it to be overproduced at Zimbabwe levels yet); granted that is not a very reliable reason for it to maintain market value, but it is the reason why it does, nonetheless.
The great advantage of Bitcoin is that its architecture provides a much more reliable guarantee why energy is required to produce it, due to its proof-of-work protocol. Granted, the exact amount of energy needed to produce each new batch of Bitcoin fluctuates over time, depending on a number of factors such as difficulty, technology available, etc., but nonetheless, it is critical that free energy (in some form) *is* required, since if no energy whatsoever were required, then there would be nothing to prevent new Bitcoins from simply popping into existence out of thin air. Anything in this universe (Bitcoins included) requires some amount of energy to produce and it would be impossible for Bitcoin (or any kind of information processing system at all) to exist if there were no energy.
If you claim that the energy that goes into producing Bitcoin is inconsequential or unrelated to its value, then I have a challenge for you: Try to create a cryptocurrency that has all the same properties as Bitcoin (distributed, secure, etc.), but that does NOT require some similar proof-of-work function for its production. I hypothesize that this is impossible. ANY currency that does NOT require energy to produce, by definition, can be effortlessly produced in unlimited quantities and therefore has no value. The fact that energy is required to create Bitcoin is not simply a side-effect of its market value, but in fact is essential to it.
To see this, consider a thought experiment: Suppose that the Bitcoin protocol did not automatically increase difficulty with hash rate. Then, new blocks would be created constantly, the block chain would instead be a very bushy tree, and there would be no consistent ledger, and no double-spend resistance. It simply would not work; it would not have value as money.
Thus, Bitcoin does indeed embody the energy that was used to create it. The exchange rate between Bitcoins and kW-hrs varies over time and from place to place, 'tis true, but that is only an example of the general rule that the free energy content of a system depends on the means that happen to be available to harness its energy as useful work - just like the free energy of a heat bath depends on what kinds of large, cold reservoirs are available nearby for a heat engine to dump its entropy into.
Far from being a mere "technical detail," the fact that producing Bitcoins requires a large amount of energy is in fact essential to its value as money.
Some related thoughts here:
http://minetopics.blogspot.com/2013/01/grand-unification-of-physics-and.html