The rukus began when scribe Melissa Rosenberg answered a question about birthing gore and sex asked by the L.A. Times. "On the fan site, on Facebook, all the comments are 'It has to be R rated! You have to show the childbirth! Gore and guts and sex!,'" she said. "For me it's actually more interesting to not see it. You know, you can do childbirth without seeing childbirth... it doesn't mean it's any less evocative of an experience." If that doesn't sound like the biggest cop out answer then I don't know what is. She should have come out and said the film has to be PG-13 as to not turn away the tweens and thus such imagery would not be suitable for the audience.
According to Entertainment Weekly, both Breaking Dawn films are confirmed to be PG-13 by Summit Entertainment. So it's a conscious decision to hide the sex and gore, not "it's more interesting that way." Because let's be real; it's not, and even the series' most Robert Pattinson and Taylor Lautner blinded hardcore fans aren't fooled.