I recently read the book, and realised it has nothing about the assasinations of Stracci and Cuneo. How come they chaged this for the film?

Joe the Greek

I always thought it was for two reasons:

1) To make the Baptism scene cooler/more violent.

2) To solidify Michael's power as the most powerful Don. Theoretically, the other Dons wouldn't have bowed down to Michael even after he killed Tattaglia and Barzini, so FFC had to have some way to show that the Corleone family was the most powerful in New York. By killing ALL the heads of the Families, they would probably have made peace with Michael and allowed him to do whatever he wanted.

Yes, the primary reason was to make the scene more dramatic, more violent. To add to the drama, FFC used a variety of killing methods that seemed a bit illogical. Neri, acting alone, kills Barzini, a bodyguard and a chauffeur with just a standard police-issue six-shot, .38 revolver. But earlier, Rocco and an associate use M3A1 "grease gun" submachine guns to kill Tattaglia (and the hooker he was in bed with). Dramatic license, I suppose.
The probable reason that Cuneo and Stracci didn't die in the novel was that they may not have taken a direct role in any violence aimed against the Corleones--but Tattaglia and Barzini did. Michael may have spared Cuneo and Stracci because he figured that, having killed the other guys, C&S would be scared enough not to cause any further problems. He may also have needed an alliance with them to cement his role as undisputed boss of NY Mafia, and thus to pass on the title to Clemenza when he moved to Nevada.

Yes, like Turnbull said, there was no reason for them to die in the novel and the scenes of them dying were for dramatic purposes. I do like Waynethegame's interpretation also. I think the main reason it happened is because it worked. On the big screen you can switch to different scenes and build the suppense but in a book you cannot.

exactly right. In the Novel the weren't killed because they did not support Sollozzo and they didn't take an active role in the New York Family War.

They werent really mentioned in the book too much(if I remember correctly).It was sort of a- reader meet Cuneo and Stracci, shake hands.... now forget all about them.

I always thought it was unfair on poor old cuneo and strachi, they didnt do anything!

I LOVE the baptism massacre dont get me wrong, but wasnt it a bit improbable, I mean Barzini, Strachi and Cuneo were pretty decent seeing as they all had security with them, but wouldnt Moe Greene and Tattaglia have some sort of bodyguard, like when sonny was visitng Lucy, 3 or 4 guards with guns? surely Rocco couldnt have got a to Mafia dons room that easily, as for Moe, not a sight of anyone, unless the corleones bribed his own bodyguard to shoot him (as we never do find out who shoots him)