It's hard to quantify, but it definitely helps when you feel like you know what someone's like from reading their comments.

A text application form is such a low-bandwidth source. Reading the applications, we feel like we're just starving for information about what the people are really like. So any additional context helps a lot.

Would it be possible to specifically mail those who were rejected?I do understand it would be time consuming for you guys, it would be really helpful to all

It would be less helpful than you might think. Strange as it sounds, there's often no answer to the question of why groups are rejected. I tried to explain it here: http://ycombinator.com/whynot.html