There is a big difference between having a nice voice and being able to sing, A VERY BIG ONE. Having a nice voice is great and all but you don't necessarily have to have a drop-dead gorgeous voice to sing well. You do however need technique and training to be able to use a beautiful voice.
Last last year I was watching over some old DBSK performances and I came across this performance of Tonight (we'll get more in-depth about their vocals on this song when I publish the re-written version of my DBSK commentary):
It literally hurt my ears and my throat just listening to it. I know I like DBSK and I know I've said that they have gorgeous voices but back then, they had no idea how to use them. No wonder SM had them mime - they simply didn't know how to sing. Yeah sure the recordings sounded fantastic but recordings are nothing compared to live performances when you're looking at vocal ability, they always have and they always will be. Doesn't matter if the song is processed like crazy or not, when an artist sings in an uncontrolled environment without any machines changing the sound of the vocals that's the true measure of ability.
Although with the advent of studio technology namely overdubbing, live performances have been demoted - they're just as vague as recordings are when it comes to vocals. Overdubbing is an industry standard now, my dad says that most of not all pop concert DVDs are put through that process.
What is it? So let's say you have a concert with the audio (already processed on the spot, but not so much) and video recorded. Before that goes on a DVD the artists go back into the studio and RE-RECORD THE VOCALS. They're not put through as much processing as album recordings go through but they're still recorded in a controlled environment, mixed and mastered - those things make the recording as far from 'live' as you can get. They then mute the video and then slap the re-recorded vocals mixed with the sound of screaming/chanting fans on top of it. That is your standard pop concert DVD. So years after that performance of Tonight, here's a studio-processed and leveled 'live' version:
Spot the difference? Yes, the boys may have learned some form of technique over the years and they really have improved but the audio is too clean, too leveled to be 'live' and not put through some kind of studio trick. Say what you want to say that this wasn't put through anything but if you've been to a live concert you know what it sounds like and you know the difference between un-processed, raw vocals and vocals put through God knows what process.
But I'll save the rest of my ranting about DBSK for version 2 of my vocal commentary of them. SO ANYWAY.
In the same way that there's a difference between having a nice voice and being able to sing well, there's a difference when I say this person is a good singer and/or has a nice voice. A good singer has technique. He/she may not necessarily have a nice voice but knows exactly how to sing - whether or not the voice as a voice is nice, the end product will be decent.
If you have a nice voice, you may or may not be a good singer. A nice voice will do if you're young and all but as you get older you're expected to learn technique - if you don't you're not a good singer, you just have a nice voice. That voice has to be used properly because if it's not, then the end product will NOT be decent.
Which is why when I do my vocal commentaries I always say 'my favorite voice in *insertnameofbandhere*' and NOT 'the best singer'. I judge vocals on those posts - not technique or whatever else.