Why?

A couple of nights ago when I was in bed and starting to close my eyes, my brain started to think its usual weird and random thoughts. Here is what it came up with, on the topic of messed-up English grammar:

Why do we call people who originated from Japan and Vietnam"Japanese" and "Vietnamese" but U.S. people "American" instead of Americanese, and people from Australia "Australian" instead of Australese?

I asked the hubby and he said maybe Asian ethnicities end one way, and European ones end in the other way. "But," I said (ready with a counter-argument as usual), "why are people from India 'Indian' then?" For this he had no answer. That's right! No answer. Where is your magic formula now, husband?

Then he suggested maybe it's because the name of the country ends with a consonant? "But," (here comes my other counter-argument) "how about ........" and at this point it took me a while to think of a country which ends with a vowel, but doesn't end with "an" when you talk about the people from it, or some country which ends in a consonant but the people are not "somewhere-ese." Then light bulb turned on! China! Why aren't China people "Chinan" and why are they "Chinese" instead?

Then my Russian sat up and was confused. He said "Wow, you are having some really really deep thoughts over there. But seriously, how about we just go to sleep now?"

What a lame Russianese husband.