Oh, it had EVERYTHING to do with business. I think the rant was simply Roth's way of telling Michael to back off. He knew that Michael had his reasons for killing Moe Green - skimming off the top, publicly humiliating Fredo (and the Corleone Family by extension). Roth let Moe's murder slide because he knew that Michael had good reason for doing it, and even though he loved Moe, he never retaliated.

I believe his rant is Roth's way of telling Michael to back off. He had his reasons for trying to kill Pentangeli, all that trouble with the Rosato brothers. And Michael shouldn't let the murder of Pentangeli get in the way of their future dealings.

Roth let Moe's murder go, and now Michael must let Pentangeli's go.