Image still matters. It's just that it's not the same image that matters everywhere. Wall Street? Bring a suit. Silicon Valley? Go for the hoodie, or the same outfit (copy) every day.

Both signal that you're part of a specific tribe. There's a reason major tech conferences are a sea of "jeans & T" people, and it's not just the comfort.

You're completely right that image is not a substitute for quality, but when you're selling something, you ideally want a bond with the customer. So, if you sell to Wall St., look like Wall St. If you sell to engineers, look like an engineer. If you don't sell, wear whatever you like ;)

That's why HN can get away with minimalist design - it's not selling anything.