I definitely think it is culturally based. In Portuguese diminutives, if not really overdone, are seen as sweet and gentle.
Diminutives in general really do stand out in Canada and not in a good way.
Not a teachie.
(My attempt at a diminutive and jokkie!... Did someone say something about a slappie?... )
I'd take a cuppa to mean tea not coffee. I don't know if other BrE speakers would do the same.
What do you think of 'all righty'? The word crept into my vocabulary after watching Sex and the City, where one of the characters kept using it. I wonder if it sounds somewhat idiotic to you; it sounded nice to me :)