Let's see.... a solid resonance free design(both in terms of the cabinet system and internal acoustic space/volumes) is one critical factor.... and simply .... no full range speakers exist at a low price point with this feature of which I'm aware. This is just one relevant factor, but it's a critical one for a high performance speaker(and the 802 meets all factors, btw, for a high performance monopolar speaker).
It's really irrelevant if one likes a truly neutral speaker like the 802D in it's natural state/response(which btw does not have a metal tweeter.. but that is a myth in any event about metal tweeters.... ). I don't like the sound myself as it is. But hey.... when you start out with such a neutral speaker, you are able to get just about any sound you want out of it with precision DSP EQs. Something very few speakers in the world can offer. The main issue with true neutral speakers is the dead flat treble. In reality, it needs to be gradually tapered down to sound natural as measured from the listening position - and this is not my opinion - it's based on multiple credible perceptual studies. But anyways, the speaker offers a true neutral starting point and full range, low distortion, dynamic capability. I'm not aware of any speaker by Polk offering any such neutral performance. In fact, most companies don't offer any speakers suitable.
One can, in specific instances, modify a speaker that offers a certain set of performance characteristics, but not all of them, to later include all of them, thus converting it to a high performance speaker. Why not at least a few manufacturers go the full tilt at a reasonable price point.... I really don't know.
-Chris