You are confusing different levels of argumentation.
The rules clearly imply that you may NOT bid 14 after a 13. That's a fact.
You are arguing that anyone with a bit of common sense should be able to understand that if one may bid 14 after a 14, one should also be able to bid 14 after a 13. That is correct, of course. But basing rules on common sense will always lead to problems, misunderstandings and arguments, not only in an online forum, and should thus be avoided.