I totally agree. Football players today (from middle school, highschool, college to the pros) are so much bigger, stronger and faster than in the past. I'm only 30 years old and graduated highschool in 1994 and remember that a player 200 lbs and 6'1 was considered to be "big". Today, that same size player is one of the average to smaller players on the team. OL'men in highschool are every bit of 6'3 and between 285-300lbs.
Many of the top ranked college teams of today (in my opinion) would dominate some of the great championship teams of the 50's, 60's and 70's. The athletes are physically superior. The speed of today's athlete from position to position has so dramatically increased over the years that I don't think the teams of the above era's could compete. They would not have the team speed to match up with today's athlete's. Also factor in the size and strength difference and you'd probably have a blow out.
Kind of like comparing homerun hitters of today's time with that of Ruth, Aaron and Mantle. The game in and of itself hasn't changed but the players that play the game certainly have changed.