Agreed. Just for "stroke accuracy" purposes, I like to put a ball near the center spot on the table, freeze the cue ball up against the either foot rail or the head rail, and hit that straight-in shot at various speeds -- from normal "optimum stroke" speed, to near as high a speed I can muster accurately, back down to lag speed (i.e. the object ball just barely makes it to the pocket). By far, for those that don't have a good stroke, the lag speed is toughest, because the slow speed exposes stroke anomalies to the light of day.
I think a lot of the reason that long straight-in shots are difficult for some people, are due to two problems:
1. Stroke (discussed above)
2. Aim.
In the "Aim" part, I think some people get "lost" somewhere in the "meat" of the ball. Meaning, that edges of the ball are easy to see and aim at, but when one is trying to find the exact center of something -- especially at a distance -- they lost track of what "center" is. You have "this edge," and "that edge" (of the ball, left and right edges respectively), and a bunch of "stuff" in-between, where centeredness is difficult to find. Part of it may be due to parallax error, part of it dominant eye issues, and part may just be poor head/eye alignment (or shall I say alignment that is just a weeeee bit off, that, at short distances has no effect, but at longer distances comes into play).
Straight-in shots are not "difficult" or "hard" (as the OP says); it's just that they require a little bit more attention than "first off-the-cuff" dismissal of the shot may say in one's mind.
-Sean
I agree that people might be getting lost trying to aim at the center of the cue ball. But for a long straight in shot all they have to do is aim at the edge of the ball just like on cut shots, JUST THE BOTTOM EDGE, where the object ball meets the cloth. That is definitely the center of the ball. Is that not the same reason some of the Filipino players aim at the base of the cue ball? Well one reason is to hit center and the other is that when using draw they would rather be bringing their cue tip up to be hitting below center than bringing it down ,where it's easier to miscue
That's also the reason why it's harder to hit center when the cue ball is frozen to the rail and you can only see the very top of the ball. Just my thoughts.