Why does pulling out main speakers from wall improve sound?

As I reflect back on all the hours viewing system set ups as lovely as they are with all those expensive components, I dare say most of these pictures have the speakers pretty damn close to the wall.  Dealers Display the speakers pretty damn close to the wall.  Then I began noticing a few set ups where the speakers looked weird being pulled so far from the wall. 
 

My large basement on the habitable side has my speakers right in the middle of the room and they are older and they really fill the room extremely well. I thought it was just the speakers but it was more than that.  In my other rooms and systems it's tougher to get those speakers very far from the walls, but I am rethinking things with a goal of pulling the speakers way the hell away from the walls.  Rectangular rooms are difficult where the long wall is being used for the system.  Points of egress and windows and doors make it difficult to use the Wall on the short side of the room for the system, very sad.

@aewarren ,

“I suggest you find a new dealer”

agreed. 

It is generally suggested that the front of the loudspeaker be placed 3ft (approx 90cm) from the front wall as a starting point.

The midrange is approx between 3khz and 90-100hz

The wavelength of a 200hz frequency is approx 171.6 cm. The half wave would be 85.8cm (approx 34.2 inches).

The wave is spherical in nature, so half the wave wraps around behind the loudspeaker and the other half wave is in front of the loudspeaker.

The lower frequencies of the midrange lie between 400hz and 90-100hz. 

As the loudspeaker is moved nearer to the front wall (2ft) the lower end frequencies get reflected off the front wall - as a result these lower frequencies reinforce the lower frequencies of the front half of the soundwave and we begin to hear muddiness in the midrange.

a simple test would be to - with your back to the front wall start speaking with a consistent loudness - now slowly walk away from the front wall until your voice sounds more natural  (ie: without the reinforcement of the lower midrange frequencies). This too would be a good starting point for the placement of the loudspeaker.

I hope this helps.

Reduces early reflections which are death for soundstage, imaging and detail.  Also proximity to walls boosts bass levels above that intended in many cases. 

SBIR - Speaker boundary interference response.

As noted, perhaps not fully correct, but as the frequency drops for a dynamic speaker, the radiation become omni-directional. The wave reflecting off the front wall is reflected, with not a lot of attenuation, and then cancels the front wave of the speaker. The critical distance is 1/2 wavelength as that will be completely out of phase.

Ideally you want to be far enough from the front wall that the round trip distance is > 1/2 the wavelength of a fairly low frequency. Put another way, the distance is > 1/4 the longest wavelength. 3.5ft, and you just created a suck-out at 80Hz. Even at 5 feet, you are still hurting important bass frequencies, and this is not stuff easily corrected if at all with DSP.

Counter-intuitive, but the solution is to put the speakers closer to the front wall, and then treat the walls with absorption. Not those those trinkets I see in audiophile pictures that cover a small portion of the wall. You need to cover a good portion of the space behind the speaker, and the absorption need to work at a low enough frequency to prevent the SBIR cancellation. You will get boundary reinforcement by being close to the front wall, but this can be corrected with DSP.