Really? Wear a suit to your next startup interview and see what the negative reaction is. I worked at a company where anything other than jeans was frowned upon. You know what, in August I'd rather not wear jeans. Dress pants are way more comfortable (hint, they breath better).
A few years ago I was working for a west coast tech company (not bay area) and was regularly wearing long-sleeve button-down shirts (without a tie) with khaki pants.
A few coworkers said something to me, but I didn't think anything of it because (from my perspective) they didn't care about their own appearance. Then my boss told me that the company actually didn't have a dress code and I didn't need to dress like that; I assured him that I was dressed that way because I liked dressing that way. Then HR talked with me. That's when I finally took the hint.
The dress codes that most people are familiar with place a lower-bound on how you can dress. "No shoes, no shirt, no service", or "You're a groomsman, you can't show up to the wedding in a t-shirt you lunatic". The tech industry has a dress code, but it places an upper-bound on how you can dress.
My humble conspiracy theory? Upper-bound dress codes encourage social stratification. This is desired by people who are in power, but are surrounded by very clever and moderately well paid people (developers). Imagine if software developers stopped thinking of themselves as "others" and started assuming the role of respected professionals with all the social standing a respected professional typically gets.
