If you hear any D-lineman interviewed, they always say the O-line holds on every play. Just a random matter of when it gets called or not.
Holding gives the referees the too much of an opportunity to control the game. Maybe the NFL needs to go back to the days when linemen had to keep their hands inside their shoulders and couldn't put a hand on a defender. Just kidding. I don't see how they blocked pro caliber defenders in those days. No way they could block the athletes playing the game today.
The holding call that I don't understand is when an offensive lineman pancakes a defender and falls on top of him. I saw Leonard Davis get called for that 2-3 times during his time in Arizona and saw it called in a game just a couple of weeks ago.
The holding that almost never gets called is grabbing the jersey and shoulder pads on the outside of a defenders shoulders. Wide Receivers do that all the time. Like you guys said its hilarious to see a photo or replay of a great run with an offensive player in the picture with both hands full of a defenders jersey two feet from an official.