I listen to more than a few singers to whose voice I had to get used to, but then I grew to like it. On the other hand, I'm instantly put off by singers with perfect, radio-friendly voice.
Like David Byrne said, it's easier to empathize with a singer who isn't perfect. You're more likely to believe him.
I'm very much into my singer-songwriters. A singer who only does covers, well, may make great music, but I don't respect them as much as people who can write their own stuff (and do it well). Even a cover sung by a proper artist (singer-songwriter) scores higher with me than a cover sung by someone who only sings covers (or stuff written by others for them).
I dunno, for instance I respect Johnny Cash as much as any singer-songwriter, even though larger part of his oeuvre consists of covers. Just listening to any American recording makes it clear why: through his performance, he rewrites the subtext of the song. While I like good lyrics as much as the next guy, I do believe that music is more defining of the message of the song, and through covering, you have a chance to change the point, from tweaking it in tone to completely turning it upside-down, which is what Cash was doing.
Sure most of people who cover songs are just paying tribute or buying time, but if you're good, covering may as well be equal to rewriting the song.
I don't liken Playing standards to covering a song. Plus aside from Jazz I haven't really looked into a lot of the standarding of the day.
Bah, standard is just a song that is old enough.