Another factor is the application for the speakers. If the speakers are for a small, acoustically controlled room with one listening position, than it becomes pretty easy to buy more than what is called for. In that situation, a good pair of studio monitors and a tight, controlled subwoofer will get you a flat frequency response, and that equipment won' cost that much, relatively. If the speakers are for a large room with restrictions on where they can be placed, then the budget to get something that can achieve a flat frequency response has just multiplied dramatically. And that is just frequency response, we aren't talking about other things like dynamic response, transient response, on and off axis response, imaging, etc.
It also depends on your personal priorities. It can cost a lot to achieve a acceptable sound for some people, before diminishing returns set in. And, as has been said, an acceptable aesthetic is important too. It all adds up pretty quick.