Put simply - no, that isn't how the rules work. It doesn't have to be Clear and Obvious. You're applying a section of the guidelines to a part of the laws where they don't apply.
The rules are very clear that for line decisions, it's either in or out. You just make the call based on the balance of probability whether you think it's in or out, that's all there is to it. The referees are just following the rules.
Now are the rules a load of shite? Almost certainly, but that's not really what I'm arguing here.