When I worked at Intel there was an engineer who had what I can only describe as "Fraggle Rock Hair". He was a white guy, and he had his hair braided into thin, dread-locked cornrows. Each one protruded upwards from his head, surrounded by bald skin, and had ribbons attached to them. He wore T-shirts and shorts and Teva style sandals almost all year long. It was like a more extreme version of the haircut Perry Ferrell had when Jane's Addiction first came out.
The guy was evidently brilliant - although his fashion sense was a little radical for the more conservative culture of the central valley than it would have been in San Jose.
There were lots of exposed tattoos and piercings and shorts, sandals and t-shirts were the typical uniform. There were also a lot of guys with bad grooming habits. Bad , unbrushed hair far overdue for a cut, unkempt beards and stubble, in stained khakis and wrinkled tech-company logo polo shirts. It wasn't uncommon to see executive staff looking pretty disheveled and haggard looking.
It is a company where end results are the culture - where the emphasis is on knowledge and production.
My wife worked for a company that made programmable chips with embedded compiled basic interpreters for robotics and automation projects. She went to all the big trade shows. She met the guy who owns Fry's at one of them and worked out a deal to bring this product to Fry's retail locations. She said he was overweight, with poor hygiene and grooming, and wore a dirty track-suit to the convention. She was shocked. The guy was probably the richest person at the convention, and looked homeless.
I think the emphasis on professional appearance can be misleading. This is why salesmen dress in nice suits. It earns trust and causes you to judge their integrity and professionalism differently. Lawyers wear suits, too. So do bankers. See a trend there?

It is like a magic trick. I put on a nice shirt and tie and a jacket, and suddenly, I'm "better".
My current employer has a business professional dress code, no jeans, no T-shirts. The company that acquired us recently has a business casual dress code. I'm interested in seeing how this all shakes down over the next couple of years.