+1 to those defending Wal-mart. It's a discount department store, not a gun shop. And even gun shop people screw up decisions like these.
That said, my local Wal-mart has a couple of very knowledgeable employees at the sporting goods counter.
I see no reason why a newbie can't handle an AR as easily and safely as an 870. It's accurate. It's low recoil, softer than my reduced recoil loads (which I bought at Wal-mart). They're not that complicated- I'm pretty sure my 9 year old could read the manual and understand it.
In any case, I think a gun owner should seek some level of training. IMO, steering a new gun owner toward training is more important than steering him toward a particular type of firearm.