Maybe the biggest difference is what happens between Sunday through Monday. Practice styles have been adjusted. With additional scholarships and exceptional depth, practices were more physical in days past. The "old school" mentality saw more tackling in practice, more scrimmage situations, and a much more treacherous spring practice routine.
The NCAA wasn't as hands-on, and schools would be in full gear basically all the time. Hours weren't as regulated. The coaches decided when to back off rather than the NCAA saying when to back off. I am always amazed when I talk to the Hayes/Bruce players describing their spring practices. The coaches knew they had about four or five months to rest up those injuries -- big or small. "Let's scrimmage!" was their attitude.
On the flip side, the Cooper/Tressel era doesn't have a walk in the park. Where football has become more difficult is the year-round workouts, most especially, the summer workouts. Players have always lifted during the winter and spring. The sunrise services have been part of every coaching staff's plan, but in today's world, nobody goes home to work out on their own come summer time. You work out with the team.
The structure around those summer workouts is incredible. Players need to hit certain targets with certain weights and run certain times. In other words, an "I'm tired so I might cut things a little short today" mentality won't cut it.
You want to impress your strength coaches and your fellow teammates with your performance. Ask anyone who trains about working out alone versus working out with a partner or group. A competitive environment with other people usually drives better results. Ask the joggers. Ask the lifters. Ask the swimmers. Ask the cyclists.
This isn't to say the players 30 years ago didn't beat their bodies up over the summer. Nor am I saying practice is two-hand-touch in today's world. Football is still football, and getting in shape is still getting in shape, but the evolution is interesting to follow.