People would possibly get less agitated about which words are classed as "common" if the terminology was different.
Suppose the words in the puzzle were either category gamma or category upsilon, where category gamma words are those that just about everyone who plays the game is likely to know. You think of a word - you know it quite well, so maybe it's a gamma. You play the word and find that it's upsilon. Looks like the word is not so well known everywhere. Either that or the idiot running the site has given it the wrong category. Either way, it's no big deal.
I'm probably repeating myself from earlier discussions, but if a word comes up in italics, it's not being insulted. There's no implication that it's a B-grade word, used only by a bunch of losers. It's just a category upsilon word, one that some players mightn't know... only we call it "rare" or not "common".
Also there's no intention to insult any nation, or block of nations, or linguistic-cultural tradition. Just as some people seem to have a feeling of loyalty to a word, that causes them to be incredulous that it isn't called "common", so it seems that sometimes people have an animus towards a word because of its origin. "Well, yes, of course I know that word, but it's an American word!"
In considering words that have variable usage around the world, I generally concentrate on the US and Britain. This is my reasoning: If a word's not common in the US, it's not "common" (in the Chi sense). If it's not common in the UK, it's not "common". If it's common in both countries, it's "common". English-speakers outside those two countries will probably know the word from books, magazines, TV shows, etc, even if they don't use the word themselves.
(If we were scoring words based on population figures, we would have to concentrate on Australian usage, since my website statistics show more users come from here in Oz than anywhere else. This might make things easier for me, but it wouldn't achieve what I'm aiming for.)
I'd be willing to change my idea of "common" words if someone could persuade me that it would improve the game. But my current feeling is that any broadening of the category would tend to defeat the purpose of having a "common" category.