In High School football, we had one extremely strict rule during practice "don't tackle the quarterback during practice". We could hit the living f* out of anyone else during practice sets, but QB you could only sort of "hug"- the reason behind it was they were hard to replace. Guess it just adds up over the year.
And yeah, they also don't wear as many pads. The shoulder pads the wear are extremely small, and usually they don't protect any part of the rib cage. In fact, in general you'd be amazed how many NFL players forego padding they're supposed to wear... NFL players actually don't protect the family jewels for whatever insane reason:
http://www.nytimes.com/2012/12/09/sports/football/helmet-check-shoulder-pads-check-cup-no-thanks.html?_r=0