And an Aussie will answer
I think I'm fairly qualified as I've been following the NFL for 15 or so years now and know enough about rugby to comment (although I'm not a fan).
Some players in the NFL can "step" (juke) and "palm" (stiff arm), but they might be a little more subtle than in rugby. This is because the NFL is just a faster game (once the ball is snapped and a play is live, not in general). The players are faster, more agile, and 'moves' are going to be executed quicker, and defenders are going to be tougher to out maneuver. The defense is also set in layers, so it's not often you're just required to dodge or take out one defender at a time. In rugby, since it is a man to man style game, all you really have to do is beat your guy and you have a nice run. In the NFL, you beat one guy and another defender is coming in for your legs from another angle out of your vision.
Also, you have to remember in the NFL every defender is focusing on the ball carrier. Defenders can be far more aggressive in the NFL since there is only a remote threat of a lateral (a pass in rugby), so they can basically all come down and attack one guy. In rugby the game is far less aggressive on the defensive side of the ball and you have to play with caution - too aggressive and a dummy will kill you. You have to stick with your man and keep your place in the line. Once a player has the ball in the NFL, it's basically the human version of demolition derby. The padding also most certainly serves as a confidence boost for defenders to fly in hard, but in general I think the "pack" mentality of an NFL defense proves difficult to evade.
"Scheme" is also a huge part of an NFL defense, and I think this is the part mostly overlooked by outsides to the sport because there isn't anywhere near the same level of scheming and planning involved in rugby. If you've got a guy on offense who has the ability to juke and weave his way through a defense, the coaches for the defense will do their best to focus their defensive formations and matchups on him, so whenever he gets into open space with the ball, defenders will be ready. This is probably more relevant to pass catchers than running backs as rushing is slightly less about the scheme than it is about man to man battles, but you get the idea. The extent of scheming in rugby doesn't really allow players to defend a particular player any easier than if they had no scheming at all (which they don't really, not in the same sense).
Lastly, you have to consider the NFL is a true elite sport where only the best of the best make it through, so the quality of defenders from top to bottom is probably higher than rugby. Rugby has the best of the best too, but from a far smaller pool of potential players, only a handful of which would be considered world class athletes.
Really though, despite all this, there are still more spectacular runs in the NFL than any variation of rugby I have witnessed. You've got guys like AD, Chris Johnson, Desean Jackson etc making runs you won't find in any other sport. The problem with rugby as a sport, in my opinion, is the lack of 'attack mode' on the defense (outside of kickoffs), and the general lack of identity on defense. In rugby, defense serves to stop the other team so the same players can get the ball back and score on offense. I'm sure some rugby players love to tackle and hit, but there's not much defensive pride and skill on offer individually. In the NFL, defense is a livelihood and a mentality, a part of the sport players focus 100% on, and this makes for more skillfull, aggressiveness defense, and hence more excitement (providing you can stay interested between snaps as an Australian viewer).
Anyway, didn't mean to go on a NFL > NRL etc rant, but I think it's a real shame more people in Australia don't pay attention to the NFL. It seems to be gaining some ground though.