Yeah... i didn't buy it there but didn't feel like debating. (I'm a former college physics major.)
Higher release velocity exactly equates to higher functional arm strength. If someone has a "stronger arm" but lower release velocity... he doesn't really have a stronger arm. In given conditions, the time it takes the ball to get to a receiver downfield is determined only by the release velocity, release angle, and spiral. (A poor spiral can cause the ball to decelerate more quickly.) Unless one QB deliberately arcs the ball higher than necessary (not an issue that Rosen has), if two QBs throw to the exact same spot, the one with the higher velocity will get the ball there more quickly.
The fact is that Rosen has well above-average velocity, therefore he has well above-average arm strength.
Now, why would anyone say he has only "average" velocity? The only reason i can think of is that perhaps in game situations, as opposed to the throws he made at the combine, he doesn't always deliver the ball with his full arm strength. I would think that applies to every QB, who in game situations can't make all throws from a perfect stance in a clean pocket. Maybe it applies more to Rosen than to most - i don't know. But it just struck me as strange to see him described with "average" arm strength, then to look up his actual numbers, and find that he has well above average velocity.
...dave