[paulsutter]

I'm saying English speakers never realize the two sounds are different until someone points it out. Of course we can hear it, the sounds are very different.

It's easy to think that the way we think about sounds is perfectly natural, except that it isn't. The reality is that it's all relative. I'm sure the tones in Chinese come naturally to you but to the rest of us it's a challenge.

As for R and L, Japanese speakers can certainly hear the difference, but it's hard for them to remember or pronounce the difference. Believe me I've tried to explain it many times, and when you try you realize the difference is more subtle than we always assumed.

Korean has more vowel sounds than English. We can hear the difference, but feel convinced that it "doesn't matter" and that "those sounds are practically the same". And it's devilishly hard for us to consistently get the sound right. And that's what R and L are like.