Mercurial storing deltas is just an optimization (sometimes it stores full snapshots): all manifests [1] refer to full file content, not deltas.
Let's put it this way: the key feature of DVCSes is that they store explicit relationships between a particular commit and its parents. This makes it trivial to reconstruct actual changesets as per my definition, which in turn makes merge machinery much more reliable.
Okay, that I can agree with. I just think it is misleading to say they are based on change lists since changelists can be derived but are not actually stored. (And in the case of git at least, the changes you derive may not be changes that a human made, per se (in other words, those changes are the output of rebase.))
Let's put it this way: the key feature of DVCSes is that they store explicit relationships between a particular commit and its parents. This makes it trivial to reconstruct actual changesets as per my definition, which in turn makes merge machinery much more reliable.
[1]: http://mercurial.selenic.com/wiki/Manifest