These are fringe cases. LeaveBuster is keeping track of repeated, repetitive leaves within a reasonable time-span, not punishing someone with extreme measures just because he left once or twice within 6 months. Therefore:
1. It happens rarely enough to not make LeaveBuster angry when it happens.
2. This happens, but if someone is "surprised" by many "sudden" DC's within a week, then really, he should have seen it coming that there's a serious issue once the second half of the week comes in. I'd still consider it a fringe case.
3. See 1.
4. That's a difficult one. But a child can predict when it's getting busy with the parents over time. If one knows that they're eating together at 6 PM, he shouldn't start a game at 5:45 PM. Unpredictable situations are, mostly, rare enough, although that depends on each one's parents (most of the time, you find a window of opportunity, though).
5. The weakest argument of them all because this is entirely at fault with the one who forgot said rendez-vous. If someone can't remember important stuff, then there are enough items that can help with remembering them (Mobile phones are pretty good with that).
These fringe cases are opposed to the many cases where people are griefing. If something isn't punished for being a jerkass, he'll not change within the wide world web.
Again, in case of TL;DR: LeaveBuster searches for patterns and these arguments don't provide a reliable pattern.