A couple reasons. In Hank’s case, first of all, that was the point of the story. For all that Jim Shooter says that he never intended that slap to be drawn in that manner, the story he was telling was about Yellowjacket’s slide into becoming a villain. So that moment was a step in that slide, and considered under those terms–not just as a moment but in terms of its aftermath, and what it did to Hank’s relationship with Jan and with the Avengers. In other words, it was a bigger moment, and about that moment in a way that Reed striking Sue when she was possessed by a super-villain simply isn’t. Secondarily, in the canon of stories he’s appeared in, there are relatively few truly memorable Hank moments, whereas guys like Spidey and Reed have far more of them. Consequently, Hank’s moment was also proportionally more important to Hank, more defining of him for the readership both then and since, than any similar moments with other characters.