What's more important, is I don't understand how anyone could possibly improve their 30 second impression.
I guess it could be that you believe this to be the case, and are remembering wrong. Why don't you note this down after 30 seconds, and then check it only after you make a decision to see if you were correct?
Companies would like you to think this, too, and law makers would very much like to think that their rules regarding non discrimination have any effect. The real situation tells another story.
But it's OK, companies can just include a nice stock picture of an ethically diverse group of people in business attire working together, an all is well.
This is not actually very hard: start with good grooming, nice clothes, posture, confidence.
Of course, this doesn't change the fact that the hiring process seems... odd.
Appearance is important, and I've never been in an interview situation where it wasn't? Unless you're insinuating choice based on ethinicity (more aimed at _pmf_'s response to your comment). Which is completely irrelevant, as are accent/sex/other discriminatory factors that make zero difference to how someone is likely to work within a team.
As I've said in other comments, there is a serious element of external preselection based on geography and company sector, there's nothing particularly underhand going on.
This is just plain ignorant. Every single place I have worked has had its share of everyday sexism and racism, and that includes how current employees act in hiring interviews. You claim to not notice these things, but what you are saying is that you don't consider those things valid differences that may affect how someone perceives your team or work environment. How can you ever confront issues in your workplace by shoving your head in the sand?
Given the way you're talking about making a hire/no-hire in five seconds, I find it incredibly difficult to buy the idea that you're not taking that into account. You're glorifying the snap-judgment hire.
Because most people do, and a good hiring process takes that into account and counterbalances it.