What Roth actually says is that Moe's killing "had nothing to do with business," which is somewhat different than saying it was business, not personal. Far from denying personal feelings, he is saying that he has (and Michael should) put personal feeling aside because they don't have anything to do with business.

Actually, Roth has plenty of business-related reasons - in addition to personal ones - for killing Michael. Michael had plenty of business-related reasons - in additional to personal ones - for killing Moe. It's hard to discern how much of each factored into the decision-making process.

I totally agree that it's all personal. The "strictly business" mantra is laughable. They choose their business, at least in part, because they're ready and willing - perhaps eager - to kill people. Like John Cusack's assassin in "Grosse Point Plank" - he keeps telling his victims "it's not me" but, as the movie goes on, it becomes more and more clear that killing is his career choice largely because of his personal background.