english pronounciation

have u listened to Korean pop groups like Super Junior and wonder why their English pronounciation is (way) better than the Japanese and it sounds as if English is a part of their lives, unlike the Japanese?

Sara came up with her hunch based on Korean vowel and consonants - which i accidentally deleted her sms by mistake in answer to my question - n she has a very strong point there, it's from her hunch that i'll try to figure on my side

i'm not an expert in languages but hearing from Korean TV series n Kpop songs i'd realise Korean's more rounded aka "open mouth" and stronger, as compared to Japanese which is more of an almost "closed jaw" language and there's always this issue of "r" which the standard Japanese "r" is acutally pronounced as "l (for lion)"

any takes on this?