It's ironic, because when Christina put out Back to Basics, she was kind of criticized by not doing it as authentically as Amy Winehouse, who made it big right around that time.
But now, again ironically, she fused the retro/pop thing very effectively for 2006. (She has some real pop perfection on Back to Basics.) It's certainly something people are trying to do right now. And also, it's really the kind of thing she does best, which is why the Burlesque soundtrack sounds so excellent.
In terms of Justin, I just feel like Bruno Mars does it so much better, so much more effortlessly. Better songs, better vocals, more unforced. I thought Bruno's performance of Locked Out of Heaven at the Grammy's was perfect. Just excellent.
I think one reason there's been some backlash about S&T and a lack of connection is it just doesn't feel totally authentic. Justin has to try and "work in" the smoothness and the R&B phrasing, as if he's trying to insert the soul into the songs that his voice naturally lacks. Meanwhile, Bruno already has a terrific and powerful R&B tone, and thus is free to make the songs pop and catchy.
Just my silly take on it.