People who learn English as a second language and whose native language doesn't use latin letters have an extremely difficult time reading words in ALL CAPITALS.
I was amazed when I gave a class a handout once which had sentences in all caps and they had an extremely tough time reading it.
Since many people do not read each individual letter, but read by looking at the word, putting a word in all capitals changes the structure of the word and makes it more difficult to read.
I don't think Russians or other people that use the Cyrillic alphabet, or Greeks have the same problem - so I believe it's not the different character set, but the ideograms.
Learning a language as an adult is hard, I just wonder if it might have something to do with that. (I never had problems reading German or Portuguese in all capitals, or other languages I've tried learning, but they're almost the same language as English or Spanish when compared to an ideogram)
Of all the weird English rules, idiosyncrasies, etc. that would confuse my parents time and time again, words in all-capitals were never one of them.
I'd chock this up to the Chinese alphabet.
It's all to do with what your original language has and doesn't have. My parents still can't understand why you need the word "the" or where you're supposed to use it, since Russian doesn't have anything like it.