You don't get to be head of a Mafia Family by being a nice guy but compared to Michael how ruthless was Vito?
Vito is unable to order the death of his son-in-law though it is apparently obvious to a hysterical Connie that everyone blamed Carlo.
I think It's because Vito was originally from Sicily, and Sicilians believe strongly in family, even though Carlo beat on his daughter. That's most likely why he didn't want anything happening to Carlo. Michael was an Americanized Sicilian. That's just my guess. I think Vito wanted to also be 100% sure that Vito double crossed the fam.
