I do agree that it is possible to have a good pairing of a sub and speakers which dont go as deep as "full rangers." As I noted in my original post, it is possible. When I said it takes experimentation, I did not mean just finding a seamless hand-off from speaker to sub, I also meant something about the quality, timbre and speed of the sub. As we all know speakers and character and color to the sound of a system. If 20hz - 20khz fully described the capabilities of speakers, we'd all buy store brand speakers that met the above criteria and be happy at the end of the day.
By 'experimentation' I meant having to try subs in your house and your system until you find one that *truly* matches your speakers in your room and your system, with your available placement options. Some speaker makes have good matching subs, such as Thiel for their line and Martin Logan for theirs. Others, well, not so much. Sure everyone and their grandfather sells subs, but some just don't have that magic integration with music, especially in real world systems not setup professionally.
I am not against subs, and I'm not saying they can't add something to your setup, I'm just saying it's not always simple - in fact getting bass right is one of the hardest parts of speaker / system setup. I have heard REL subs, in response to an earlier post, and they are good subs, but I would not agree that they are a good match for every setup. Rel is a company that does focus on matching subs to stereo systems, rather than just an HT focus that other subs can sometimes have.
The other factor here is that with something like the Winds vs. the Hawks, the Winds have far more to them than extended bass. Their increased resolution and end-to-end tonal balance, their superior presentation of instruments and separation are beyond what the Hawks can do. No amount of money sunk into subs will make a pair of Hawks into a pair of Winds. That was the original question.