I would say this is how football rules have changed the game more then how the players have changed.
Here are a couple prime examples
Courtney Osborne's sack on Gabbert. Osbourne keeps his head up & Gabbert turtles up before the hit causing the hit to be high on Gabbert. Flag is thrown. In todays rules he could be tossed.
http://www.youtube.com/watch?v=BvOdXcMw5xw
SJB's hit on Prudue RB. SJB dropped his head & made contact with the players helmet and the football. He was tossed from the game. 10yrs ago that was a hit that was tought. Get your helmet on the ball and good thing will happen.
http://www.youtube.com/watch?v=kmHN5ya--ew
Heres another. Notre Dame DL drops his head to make a hit & the Pitt QB does the same. Both players drop there head but the DL is ejected for targeting even though the both dropped their heads to create the problem.
http://www.youtube.com/watch?v=SCxuVXRTt3I
The rules have been changed to put the defense at a dissadvantage. You will even see obvious holding calls not made. Has anyone ever seen a RB get thrown for a helmet hit? Probably not as that is not who they care about.
http://www.youtube.com/watch?v=omhTWveotos