I think that Buscetta emphasizes Michael's estrangment from personal ties within his crime family. Those closest to Vito were long time companions; those closest to Michael were more like employees. I think it also points out the business side of Michael's machinations which lacked Vito's personal touch.

"Generosity. That was my first mistake."
"Experience must be our only guide; reason may mislead us."
"Instagram is Twitter for people who can't read."