I just can't see how that would indicate that whatsoever

It's a result of my background, mostly military college, that causes me to see the effort and pride you put into your own appearance as a reflection of yourself. I'm not shining my own shoes anymore so I'm not as strict but it's part of my personality.

But it's not just about how you do your job it's also about interview preparedness. You never know who is sitting on the other side of the table so you need to be ready to meet their criteria. If you want the job you have to convince the interviewer to hire you. Being aware of and meeting their expectations is part of that. It's a mixed bag, I'll grant because you have no way of knowing but you can try and do a little recon on the culture of the company. At least ask your initial contact what the dresscode is like. (Showing up in a suit for an interview where everyone dresses casual can be a bit embarrassing on both sides of the table.)

But ripped jeans vs nice jeans, good shoes vs torn ones, maybe a fresh shave or trim. It really is about showing, to me, that you respect the environment and the interviewer.

Do programmers need to interact with the clients a lot where you work?

I'm an on-site consultant 90% or more of the time. I sit next to my customers, see their managers every day, and otherwise present the outward face of my company. This is somewhat atypical in an IT setting, I understand, but it suits my nature. I got really tired of dealing with "hacker == rockstar" culture and its side-effects.

This factors heavily into who I am interviewing and recommending for hire as well as what I'm looking for. If I was running a development team that sat behind closed doors it would be a little different. In my current role I need people who can interact, socially and professionally, with clients directly. Without supervision. But casual dress and sloppy dress are not the same thing.