I think they're claiming that it's true for Trello, not necessarily overall. Their other products are a testament to the fact that they're happy to go the other route (lots of money from few customers) with some products.

But since they think they've found a new form of "Data structure that anyone can find helpful", they'd rather try to get everyone using it than try to specialize it for a few verticals that might pay them a lot of money for a form of it that is optimized for their business.