The difference between Ben and Cam is sheer will power. While both are massive QBs capable of shaking off pressure, many times Ben in the past just refused to give up and it was that will and mentality that would allow him to escape sacks, Cam on the other hand does not seem to have this same attitude. Your right as well regarding pocket presence, one thing Ben is so underrated for as he has such a feel for what is going on around him (most of the time) he sees the rusher coming and is able to parlay that into an escape (I swear sometimes Ben had eyes in the back of his head) and when you add his body type, it makes him so difficult to bring down. Cam on the other hand, while a great runner, does not seem to have this feel for the pressure (especially his blind side) to be able to prepare to escape from a sack like Ben. But at the end of all that, it comes down to sheer will, and Ben willed himself into many of those impressive escapes and big plays that are forever ingrained in our minds. Gonna miss him so much when he hangs them up.