I imagine because pomegranates are not Chinese, they are Middle Eastern.
As for Indian Corn it's hard to say. While certainly it was the Indians who first grew it (though I suppose you could argue that we should have changed the name to "Native American Corn" some time ago) there is the fact that for a long while "Indian" was a slang word for "fake" or "bogus" in American parlance (as in "Indian Summer" "Indian Giver" etc.) Given that "corn" was at the time I general term for all grains, and maize was generally looked upon as a lower grain, suitable only for the poor and servant/slave classes (hence the old slave saying "we grow the wheat and they give us the corn") there might have been some insult involved. It probably doesn't help that ornamental corn is usually flint corn (well, the full size stuff is, the little ones are usually popcorn) which was often considered the low man on the edible corn totem pole (you would grow it if your climate was too wet and too pest ridden for anything else to survive well, but it was the hardest to grind (you needed a good mill to do it on a big scale) and did not make the soft flour most Europeans were used to.)
As for why we do it, I think it is just a fall thing; a symbol of the harvest being in (in Europe, they sometimes would make little ornaments of braided ears of wheat and barley, I imagine for the same reason)
Speaking of ornamental corn, I've noticed it has been in short supply this year (or at least shorter supply than it usually is) with a lot of places that I would normally get it opting out. This is even truer for the kinds I seek out (the ornamental corn of the fall is the main source for my seed for the next planting season, and I am very selective of what I get) Maybe it's the bad season we had (though due to the season being off, most of the corn sold this year was actually grown last year; maturing after it was seasonally salable and stored for now) As usual, Shantz farms came through a little (though with the A&P's having been taken over by the Acmes, the number went down a lot, since only one of them seemed to decide to sell corn this year) but even there the quality is now what I was used to (I've gotten four bunches so far (so twelve ears) but only one of those was really "A" grade stuff (and I think their supply has been exausted for the season by now). There's a stand at Union Square that gave me a little of the stuff I wanted too, but again, there isn't much and I have probably tapped that out by now.
The stand in Hartsdale has LOTS of corn, but none of it is the stuff I am after (I think I found one ear I could use last year, but that was an anomaly)
My favorite corn stand there HAS gotten in some (they skipped the last two years) but this years stuff is not nearly as interesting as it has been before (what made me love that stand is that their incredible diversity of starter seed, combined with a policy of not being careful to segregate and re-planting from their leftover stock meant that you often got ears with combinations that you would NEVER see in the normal path of things, like mico sized (popcorn sized) ears of dent corn, or flour or even sweet. ) But this year it's been much more standard (maybe my heavy buying in previous years rouged out most of the interesting stuff) there's some odd colors, and a few ears with kernels that are sort of cloudy (as in approaching floury) but that's about it.
Oh and I have gotten two ears with kernels for the sugar bottle (the bottle where I put any sweecorn kernels I find on ornamental corn, with an aim of trying to make a multicolored corn on the cob of my own)
And so far that has been all (I know that sounds like a lot, but I tend to go through HUNDREDS of ears a season, that's only about couple of dozen) There is a third stand that seems to have gotten in some of the popcorn version of Glass Gem (that's good, since my old supply of the stuff on dowels dried up with the loss of A&P, but as yet I have seen no ears with a better color mix than the ones I saved from last year) and some bright red dent (maybe Bloody Butcher) which is of interest (I haven't bought any since it seems a little dull,but if I was buying corn to grow grind and eat, it would probably be just what I was looking for.)
