Well, it's not as if people that do know/should know better pronounce the Japanese character's names 100% correctly.
Especially people whose native language is English do tend to still butcher the pronounciation of the names. That's probably because English is hardly phonetic while romanized Japanese is.
The big majority of native English speakers that I know pronounce Kasumi as "Kuh-soo-me", stressing the "soo" syllable. It's however more like "Kuss-uh-me". "Kuss" being stressed and "uh" and "me" being said quickly and without stress.
Then there are names like Ryu, which are literally impossible for an English speaker to pronounce correctly unless they learned Japanese pronounciation. The R and U sound are just so different from the English ones.