I don't necessarily know if it is diet America but a lot of the Australian holidays and celebrations do feel to me (as an Australian) as slightly odd. I suspect it is because Australia is a relatively young country so there isn't a long existing history of traditional celebrations so we have kind of appropriated existing traditions.

Christmas is best example I can think of there are decorations depicting things like Snowmen and Snowflakes etc. We sing songs about "dashing through the snow" all whilst it is oppressively hot outside, its hard not to notice a bit of dissonance.

ANZAC Day is really the only holiday celebration I can think of off the top of my head that has a uniquely Australian flavor, with things like marches, Two-Up etc.