How people interact in a small business is surely different than in a larger business, so I'd guess small business is more inclined to need a culture of "we're all in this together".
I think that "everyone is as important as everyone else" is in tension with "the market rate for developer and support roles are different than our flat salary".
I think they're right about some of the negatives about "traditional performance reviews and salary negotiation". But I'd be cautious about whether "everyone is as valuable as everyone else" brings more problems than it solves.