Eh, I don't know that the characters remembering other world lines from the same Attractor Field really makes much more sense than them remembering other world lines from other Attractor Fields... ^__^;
But yeah, I can see where you're coming from... The other examples we've seen so far were all flashes from the same Attractor Field, from world lines that are relatively "close", according to the divergence meter. "If the characters only have faint memories from relatively close world lines, what of those world lines that are in other clusters altogether? One could think they wouldn't be able to remember anything at all!" That's a bit of a leap of logic considering one wouldn't know how these things work in the first place, but an understandable one. And I think the story played on that, too, actually...
In the visual novel, we only had examples of flashes from the same Attractor Field (Faris, Ruka and Mayuri, like on the TV show)... until the final scene, where Kurisu has this weird flash she can't explain regarding Okabe.
Okabe is initially surprised as well (either because he, too, assumed you could only get flashes from "close" world lines... or because he's a decidedly slow learner), but he then basically reaches the conclusion that "hey, okay, so that was possible! and I guess anybody can remember, too!" in his narration. You could make the argument that's treated as a bit of a final surprise before the curtain falls.
Now, having Okabe spell that out to the player might fly in the visual novel format (you've been subjected to dozens of hours of narration in suspended time, what's five more minutes of it toward the end?), but you probably don't want your animated adaptation to stop in its tracks for five minutes in front of a frozen frame of Okabe and Kurisu staring at each other. A bit awkward, especially for a final scene.
I think that may well be why the TV show went ahead and added that bit about Kurisu faintly remembering her own stabbing, a few episodes before the end. That wasn't in the original work, and set a convenient precedent of "cross-Attractor Field flashback" so the viewer wouldn't be too weirded out during the final scene. Of course, on the minus side, it's now easier to see the "surprise" coming, but hey...