Most of this post leaves me thinking, "Why should I be worrying about things like this?" A fair amount of it leaves me at least somewhat boggled; I suspect I'm not alone here. The idea that a user of a DVCS needs to be familiar with issues like these tells me that something is seriously wrong with the design of DVCSs.
Remember, a DVCS is a tool we use to track and store data related to a project. The project is what we are interested in: the Python or C++ or LaTeX or whatever. Git, Mercurial, etc. are just there to help us keep track of the real work. Time spent dealing with the intricacies of Git is time not spent on the primary task -- the thing that Git is supposed to help us with.
Consider filesystems, which are also tools used to manage stored data. If I'm writing some Python thing, I don't proclaim to everyone that I'm storing my work on a ReiserFS volume, and I'm thrilled by the fact that ReiserFS indexes its metadata using a B+ Tree. I just store my data.
I think a well-designed DVCS would be thought of in much the same way. Clearly, current DVCSs aren't. Something is very much amiss, folks.