I also agree with this. I like Streetlight Manifesto, and that guy's got a pretty bad voice... but he also doesn't try to make his voice sound good on the albums. I've noticed that Tom sounds normal (like he does live, I mean) on like Dude Ranch Buddha and Cheshire, but on the later albums his voice is heavily altered. And people say he's a great singer. That's what bothers me.
That being said, I don't think that a good voice really means anything. The Voice has to fit with the music. For instance I love Leftover Crack, and his voice is fucking dreadful. But it fits. Same with Mark/Tom. In any other band Tom's voice would be unnecessarily grating and Mark's would be boring. But as long as it's blink, they're both "good" singers.