I like it better this way (in the movie). Michael's thoroughness adds more weight to his statement to Carlo: "Today I settled all family business, so don't tell me you're innocent."

All family business, being settled in one afternoon. Imagine that. Would the baptism scene have been nearly as amazing if he had only taken care of three people? And if you're Carlo, hearing that phrase coming out of Michael's mouth, wouldn't that be so much more powerful, knowing that all family business was settled by murder?

Hearing Michael list the day's body count must have sent shivers down Carlo's spine. How could he possibly believe, after that, that his fate was just a permanent vacation to Vegas??