But then, I am not a native English speaker, so what do I know?
I probably should have confessed earlier that neither is mine. But judging by your last name Hugo, it is probably the same as yours (dutch).
Do you really think that end-point inclusiveness is counter-intuitive?
It was me who said that because in my opinion endpoint issues are often a mess that I feel ambivalent about: I don't think there is an "intuitive" way of dealing with them. When I said I would exclude the endpoints I was thinking of the continuous case, because it is the more general one (e.g. pick a number between 0 and 1).
I think the best way of dealing with ranges (which is what I think BETWEEN is trying to do) would be in the way SQL partition functions are defined because there are often multiple contiguous ranges to deal with. The moment you try the single out a single one of them you've got an issue with (or at least decisions to make about) the endpoints. Hugo avoided this by using integers, but coming from a mathematical background I prefer approaches and solutions that also work in, and are (or can be seen as) intuitive from, a more general perspective.
(I hope this discussion isn't undermining future questions that Hugo has planned; I see there is a '1' at the end of the question title)