I suppose some artists do consciously adopt a twang but on the other hand if you're that influenced by country music and you start exploring/singing it at quite a young age, the twang might come quite naturally as it's such an intrinsic stylistic element to the genre, in the same way that elements of soul music might come to someone who was raised listening to that genre. Also, I suppose everybody tries to mimic their idols in one way or another when they first start playing music so that must come into play also. Personally, I was told years ago by a singing teacher that I had a natural country voice/twang which I found odd because I really didn't have any exposure to the genre growing up!
In terms of an example, Keith Urban is New Zealand born/Australian raised and has that twang. I'm not too familiar with his music, but from what I've heard I think that the twang fits well.
A lot of the more contemporary country artists sing with a more subtle or no twang, for example Gillian Welch and The Civil Wars.
