1. Rick didn't go out of his way to put a bullet in anyone's head in the bar. He shot the first guy in the head for a kill shot. The fat guy got two quick taps to the stomach/lower chest or liver, then a quick headshot. Sure, that headshot could be symbolic, but it was quick enough to just be a kill shot considering the other two weren't immediately fatal.
2. The hanging zombie was bitten previously.
If everyone is infected, then everyone was presumably infected when the apocalypse started. The people on the interestate were presumably fleeing the zombies in the city, so it would make sense they died without turning. I was on board with everyone being infected and all who die from now on will come back as zombies, but the dead bodies on the interstate would be a major plot-hole IMO. I wouldn't buy the explanation saying they just hadn't been infected yet, because then... where did the first zombies come from?
Maybe they'll address it completely in the show, but from what I understand, it will probably never be fully addressed.
I don't understand all the talk about being weak and turning. If you get bit, you die from it, and then come back as a zombie, and digging a bunch of graves didn't lead to that guy's demise a bit. It's pretty standard zombie movie stuff, and I think they've even addressed that part directly. They've spoken about scratches, but it hasn't been addressed directly so far.