Probably some survivorship bias, but ultimately how you dress and handle yourself is essential, and this is especially true for people who you are meeting for the first time.

When I was in high-school we had a few teachers who's motto was "Dress for success", they repeated it a lot, and we even had a dress-up day that people participated in. I took this advice to heart and have kept a close eye on both my appearance and grooming. I try and dress sharp, always slightly at or above the crowd but never below. This translates into 'business casual' for most software jobs I've been at.

Although it's impossible to measure accurately, I can say that in my personal experience, if you're the person dressed appropriately, the people who matter notice. I've been pulled into very important client meetings, ones that were way above my position, precisely because I was dressed much more professionally than the rest of my programming colleagues who insisted that a hoodie and flip flops were workplace attire.

I've also had the experience, a surprising number of times in my short career mind you, of seeing various clients and exec types come into my office, scan the room, and then decide to come talk to me. I asked one of them once why they came and spoke to me specifically as I was just a software dev. Their answer was something to the effect of "You just looked like you knew what was going on around here."

My thought on dress is simple; I am working to make my company/bosses look good. This means that I work hard and do a damn good job, and it also means that when a very important mucky muck steps into the office to see if they want to sign some big contract with us, I appear successful and confident. If I appear successful and confident, the client will be a whole lot more likely to feel at ease knowing they're not gambling their money or time away to someone who doesn't care enough to keep themselves groomed.