Another thing is football you have people grabbing and wrapping you up which leads to twisted ligaments and such. Football you also see guys getting hit by multiple players and they can also be put into very prone areas like jumping to retrieve balls. Football players seem to be more reckless with all the helmet to helmet, horse collar tackles and face mask. Id personally would rather take a hit from kronwall then have two warren sapp sized linemen jump on top of me.
Yeah, football is a really grinding sport. Not only are you getting hit, you're getting twisted, straining against piles of extraordinarily heavy people, etc.
I have no doubt hockey hits are harder. Physical guys skating at high speeds against glass and wood? Yeah, the distance alone leading up to a hit is much greater than in football, I'd say, so the impact would have to be higher in force.
However, the two are really different and I don't think this proves either one is necessarily tougher than the other.