Consider that many tower speakers are essentially just bookshelf speakers built on top of a weak subwoofer in design.
I agree. The KEF 207/2, Revel Salon2, & B&W 800D are examples of monitor-atop-a-weaker-subwoofer in design. The tweeter & midrange are the monitor section, and the woofers are subwoofer section.
But it seems most people either don't care or not willing to accept this concept.
AJ's Soundfield Audio Overture speaker system is like that.
http://www.soundfieldaudio.net/1812-overture.html
Each Philharmonic-3 tower comes in 2 pieces - a monitor that sits atop the bottom bass cabinet, but is wired into a single speaker system so it behaves like a single speaker.
Modular speakers like Gene's $50K RBH/Status Acoustics 8T towers are 2-piece (monitor/subwoofer) speaker systems.
http://www.statusacoustics.com/8t.php
So is the new RBH SVT Modular Tower:
https://rbhsound.com/svt.php
People like to say things like "best placements", but when it ACTUALLY TRULY comes down to it, people will do what's available and practical and try to also make things AESTHETICALLY PLEASING.
As if people are going to actually place a subwoofer smack in the middle of a room if that's truly the "best placement".
And I don't know of many people who could place a big subwoofer right in the MIDDLE of the front wall.
Let's be real (like what you and I are saying). Most people have a TV atop a TV stand in the MIDDLE of the front wall. The sofa will be placed the MIDDLE of the back wall if the room isn't too big.
We won't find many people who could place a big subwoofer in the middle of the back wall either.
What most people have AVAILABLE for practical subwoofer locations are the spaces in close proximity to the front left and right main speakers, which is similar to having the monitors atop the subwoofers in the same locations as the front mains.
For example, if the room is 18FT wide, the usual locations for the mains might be 3-4FT from the side walls and 10-12FT apart from each other. Good locations for the 2 subwoofers could also be 3-4FT from the side walls (1/4-wall placement of subs).
I think one barrier to this monitor-atop-subwoofer concept is the aesthetics. I think most people think this looks ugly. Or they are just not USED to this idea. It seems very odd and foreign to them, which is understandable.
When I had the KEF 201/2 monitors, I placed them atop the Funk Audio 18.0 subwoofers using VTI metal speaker stands (with isolation cushions on the bottom of the stands and under the monitors). It worked great.
For me and probably most people, the HT system needs to not only SOUND GREAT, but also LOOK pleasing and practical.
When people do a crawl test and find that best subwoofer location is right smack in the center of the room, they are NOT going to place a subwoofer right smack in the center of the room, so people need to give it a rest with this statement.
But bottom line, there is always more than 1 way of doing things that will sound great to people.
We all don't need to do things the same way.
Darn, I feel like I'm in court or something.