I've read other articles mentioning Cassel's strong arm, as well heard others in comment mention it. Cassel may not be known for it because he's not a media golden boy like Manning, of which we're brainwashed continously by the media with how strong & great his arm is. As well, Cassel hasn't been a starting QB long enough to establish a well known rep for his arm being strong or not. Montana was in his 5th year before most began to realize his talents & strength of arm. Reps take time to build over games & seasons.
Lastly, it also depends upon opponents strengths & weakness' defensively, our coaches game plan & calling against an opponent. We have a strong reliable rushing game, of which a long passing game isn't worth the risk of interception turnovers when a team has a strong rushing game.
Manning is intercepted ALOT with his long pass game...shoot, 4 times we intercepted him in the last fluke of a wildcard playoff game with the Colts. That was the year they went on to the SB I think, if memory is correct, and statistically from a defensive point of view...they never should've won the playoff game against us. Our then so called 'lame' defense was all over the Colts. Our offense let our defense down that playoff game.