To add my 2 cents...
1) The key word in AS12's post and rule cite is "COMPLETELY"...many people do not realize this, if even one cleat is still on the outer edge of the chalk line of the box, they are not out of the box at contact
2) Your best bet of an umpire seeing this are on bunts, as you alluded to. The only time it will really be seen on a non-bunt is when it is blatantly obvious
3) Because this is not a rule an umpire can intentionally watch for (would you rather they watch the foot of the batter or track the pitch?), any benefit of the doubt will side on the batter. Simply put, this is a rule the umpire can not be wrong about if they call it (similar to leaving early on a tag and missed a base on a HR...you can not call them out unless you are 100%). If the umpire "thinks" he may have been out, it isn't being called, but a good umpire may make a mental note of the player/# that it was close and be a little more cognizant their next at-bat(s), but again, you can't not track the ball
And I sincerely doubt you have seen a batter out of the box 12 times this season...see #1 above, and also will add, they must make contact to be out , being out of the box by itself is not a violation, nor is swinging and missing while out of the box.
If you truly have seen 12 valid violations of this rule, completely out of box and made contact, then your coaches need to do a better job of coaching their batters, because in hundreds of games umpired in the last 2 seasons (HS, college, and summer tourney ball) I think I have called this once.