I think, in context, Linus was probably right. There are some situations where having 2 very different project/modules depend on common code could be hell. Just remember the multiple WebKit debacles or the BSDs. It might be better to keep an eye on each other, pick the specific updates, but have total independency. Else, you end up in commit wars and endless arguing on mailing lists.
They split off a common codebase, but they share a lot of code and patches fly across the multiple codebases without major problem. What takes the most effort is porting across big new features. But that is expected.
ESR is way overrated, IMHO.