Ive seen far more 'serious' injuries in the NFL than I ever did watching Rugby growing up ..
Thing is, are you talking about rugby union or rugby league here? The reason I ask is that union was probably always the softer sport of the two and rugby league is the far more robust, contact heavy.
Also, the Aussie league players tend to play a more rugged game than their English counterparts and probably suffer a greater number of injuries due to being more physical. For example, popped knees, ankles, shoulders and elbows are fairly common, as is a concussion here and there, and broken limbs do occur occasionally also. In fact, two players in recent times suffered broken necks, though fortunately their spinal cords weren't severed and they're not quadriplegics.
I recall when Hulk Hogan was here in Oz and appeared on our footy show. He commented on how tough our players are to go into battle without all the protections of NFL and said something to the effect that he thought grid iron players were tough, "but these rugby leaguers are crazy tough."
You are right however, each code has its own dynamics and issues, and players from each may find difficulty adapting to another. I could well imagine a NFL player finding it tough to adapt to rugby league, and a rugby league player finding it tough to adapt to grid iron because of the differences.
I won't include that Aussie Rules stuff we call aerial ping pong in this, though... cos that truly is a nancy boys game. 
Go Wigan Warriors !
Yup, they're the team I follow in the UK. We get the English Super League on TV here, so I can keep up with proceedings over there as well. Oz is hosting the 4 nations tournament later this month with Australia, England, New Zealand and Papua New Guinea vying for the title... looking forward to that, now our regular season is over 'til Feb next year.
I never broke a nail playing football but the helmet was murder on my long golden locks.
I'm taking it you didn't always have the spit and polish job you have now, then. 
So, was it the humidity under the helmet that made your hair fall out, or was it doing too many U-turns between the sheets
