I can't speak for east of the Mississippi, but this is definitely the standard out west. There are occasional glimpses of "stealth wealth" style, but most look like they forgot to pack and had to dress off of the sale rack at the local sporting goods store.
I also find it funny how mismatched they are with their wives. The women are out there trying desperately to look like the lost Kardashian but the men don't seem to notice in the least.
Not to get too existential here, but I find it odd that we live in a time in which we hear lots and lots about income inequality while at the same time upper and lower class people probably dress more similar than at any other point in recent history.
I've been in LA for 10 years now and it still manages to surprise me when I go to a nice restaurant and there's people in flip-flops and Dodgers t's. It's not like it's a rejection of materialism, though - these are the same people who can't wait to tell you about their BMW's or how they can't drink any coffee that's not a single origin bean that costs $60/lb. It just doesn't seem to be something many people pay attention to here.