Celine sings beautifully en Francais. The Quebecois vocal style has a very nasal sound, and the vocal mask placement is different and specific. The voice mask is understood or trained differently by all great singers and of course the anatomy and ability and taste of singers vary. Celine has the most spectacularly pretty and agile soprano voice, like her style or not.
Dolly Parton sings exactly as she speaks. She has a very pure and simple singing voice that happens to be beautiful. Gladys Knight is similar. Most good pop singers voices evoke their speaking voice. But trills, runs, ornaments, rasp, head and hollow voice echo sounds or pure power belts are not affectations if they are added to the natural sound. Or like Streisand or Sinatra, who are more Bel Canto singers with beautiful legato - a concentration on the beauty of the sound above all, the never ending musical phrases. These are vocal skills. Whitney and Sarah Vaughan had too many natural gifts to bother mentioning their small bad habits. When you are that gifted, you play with your voice and its power over people regardless of your repertoire. Callas. Vandross. Houston. Fitzgerald. Gabriel.
But there is personal style. Both Joni Mitchell and Neil Young could sing more traditionally in tune when they started out, but they have a flat and sharp style of singing that came later in their careers. They get what they are doing, it is their sound. Most blues singers sing a bit sharp, but just on the edge. Part of the style. Think Nina Simone or BB King. Steve Perry or Robert Plant would not be caught dead singing flat, because they wanted to pierce the atmosphere with their sound, and you cant do that flat or with foggy ornamentation. Most of the great country singers put a sharp edge on it too.
Many alt pop, rock and folk singers skate on the edge of flat singing. It can add a propulsion to the music as in early Dylan, or dirty gravitas like Johnny Cash or just plain old drug rock texture like Jagger or his ex Marianne. But it can just be bad singing like Liz Phair and Kurt Cobain, Lana last Ray. Singing flat is forgivable, but is unforgivable as an affectation.
A FAKE or affected sound is more like Gwen Stephanie or early Tom Waits, middle Alanis Morissette or all of Elaine Page. I hate to say it, but Bowie too. The natural voice can be given an accent or a false tone and vocal placement that can be sustained over a career. Done well, it is what some of the most highly trained classical singers do everyday. Done poorly you get fake country or Arcade Fire and Jennifer Hudson.
Roy Orbison, Adam Lambert, Jewel, Chris Isaak, Winehouse, Cyndi Lauper, Michael Jackson and even Cher sing within the reality of their voices, with some affectations.
Madonna was a series of seismic mutations on vocal affectations, but that is her art. She did it well. She just cant sing.
Springsteen is not affected. Nope. Call it something else. Bonnie Raitt. Dionne Warwick. George Michael. Al Green. Diana Ross. Kelly Clarkson. Ray LaMontagne. Just call them great.