Wait, avoiding 3-way merges and instead only allowing 2-way merges has been on my list of "advantages of Mercurial that are sadly lost to git" list for a while. Can you expand on what you're saying?
I've seen other systems essentially say, "Oops both versions modified this file... Good luck!" It didn't matter that the modifications were to very different parts of the file. I've never seen that in Git. Any merge conflict I've gotten in Git has been a true potential conflict, even if the resolution is straight-forward from my perspective.
A 3 way merge would have "original", "version a", "version b", and "version c", where "original" is the common ancestor of a, b and c. Mercurial disallows merges like this, but git supports them. I have no idea why git allows it.
But yes, older VCSs ignored the "original" concept, which meant diff tools could just pop up "a" and "b". Which is just a way worse idea than including the original as well.