WWE does not set the rules to what is PG and what is PG-14, R-17, etc. The TV industry sometimes makes no sense...but as to the difference, though the implication was there that Bret Hart was in the limousine, and violence was supposedly committed to him with the crashing of the vehicle, there was no graphic violence to Bret Hart. There was no camera set on Bret as the car crashed, there was no blood or violence being shown to him. There is no blood on him, he's simply slumped over. Therefore implications means nothing...and WWE are free to use them as long as they show no blood, gore, etc.
I suspect that some of last weeks beat down was somewhat impromptu and a line was crossed. Danielson was shown directly choking someone in camera which is not PG according to TV standards. Though, I'm of the opinion that WWE should not be considered PG simply because the moves in and of themselves are illustrate a form of "violence" towards the body. With WWE pushing limits, I'm suspecting that Danielson was the goat in that instance, and potentially there are others who are just as accountable for what happen. Apparently, Heath Slater almost choked Cena with the rope, but Cena warned him not to a Slater promptly stopped, this is hearsay, but as its being reported now, it illustrates that wrestlers are prone to make mistakes.
Lets be real though. WWE pushes limits. They must push limits. They may have tried to get away with one too. I'd like to speculate that someone told the NXT rookies to "make it good, make it look real." This is part of a storyline Reality is mistakes are made all the time, but its the TV watchdog and their complaints that dictate consequence not WWE, because WWE pushes limits...so mistakes will happen, heads will roll, but not live as that definitely is not PG.
P.S. Danielson will be back in my opinion IF he wants to be. There is too much behind the scenes clout here to know for sure... but if WWE want him back, they'll find a way to get him back. Plus they merge reality and storyline together, so its hard to know how things go down precisely, because there seems to be an angle to everything. We might figure it out over time.