Most film is art, not life/reality. Sound designers have to match the visual art on screen with the sonic art of their mix, and that usually includes a certain amount of "realer than real", suspending some of what we "know" about physics in order to tell the story in a way that translates to this 2-dimensional, 2-sense media.
Case in point, when we see some big impact on screen, such as a lightning bolt, we as audience members expect to hear it, much as we expect to hear the starship Enterprise whooshing by at warp speed, even though there's no air (and thus no air movement to create the "whoosh") in space. We also expect to see it match up with the visual effect on the screen; this both increases the overall impact of whatever just happened, and keeps us suspending disbelief that we're not watching a movie, we're looking through a window into another universe. Hearing a delayed sound effect might jerk us out of the director's world and wonder what's going on with the media system, and once we've left, it's hard to get us back.
The speed of sound delay would also, even in the ideal, make us feel further from the action. You see a lightning bolt hit a distant mountainside. 3 seconds later, you hear an ear-splitting thunderclap. While that might be totally accurate to the scope of the shot, in the ultimate ideal of the audience totally suspending reality and believing they're physically in this world you've created, they'll be thinking "damn, I'm glad I'm not over there", when in cinema the location of the camera can jump from place to place as needed, and the very next jump cut could put the audience right in the thick of the aftermath of that thunderbolt.
That also introduces another problem; from the previous perspective, the thunderbolt happened three seconds ago. So, when you jump-cut to the site of the impact, do you show it at the moment the thunderbolt hits, effectively going back in time 3 seconds, or do you show it in "real-time", as if the camera instantaneously moved in space while time progresses "normally"?
As a different example, let's say that, in the climactic scene of Return of the King, Peter Jackson decided that the sound produced by Sauron's eye imploding and then exploding should be accurately delayed based on the camera's distance, because the event produced a big visual shockwave and so it would be believable to have the sound hit you when the shock reached the camera. First off, at its full height that tower is almost a mile high. To have the entirety of it in frame, even as it's collapsing, without any vertical compression of perspective, the camera has to be even further away from it. So, the shot of Sauron exploding and the tower disintegrating from the shock would be unfolding in front of you, sound-effect-less, for over 4 seconds before the shock wave (and thus the sound) hits the observer at the camera. While PJ might have been able to make it work, that's a long time to be expecting the biggest explosion ever heard in Middle Earth and not get it.
Despite the practical difficulties in making these types of sound delays believable in film, such delays are sometimes used, but in "enhanced" situations; the visual effects team might speed up the speed of sound, and thus the shockwave, to lessen the time the shot has to go on before the sonic payoff. As an audience, we're not sitting there with a stopwatch and laser rangefinder to figure out whether the speed of sound is accurate in the shot; we see a big shockwave, then a short moment later we see and feel it hit us and go "whoa, this is pretty realistic".
You'll also see sound designers architecting a "double explosion". They'll engineer a big, powerful explosion sound right at the moment you see it, then the visual effects guys will put in a massive shock wave, and as that passes by the camera the sound designers will add an extra "whoosh". Or, with a slight delay (and a really fast shockwave), the designers will engineer a small crescendo to the big boom, so you know it's coming. These little audio tricks aren't what you hear in comparable "real life" events, but then again, neither is the sound of a movie punch or a movie explosion compared to the real thing.