What makes you build a system around an amplifier?

For me it was my first SET amp. It made my solid state amps sound grainy and etched by comparison. It's kind of like how I never noticed crossovers until I got a single driver setup. Nowadays, unless the crossover point is below around 1.5hz, I hear the problems with crossed over drivers. 

Back to the SET. There was a loss in slam, but this is a bedroom system so I don't play a lot of slammin' in your face kind of music there. The sound stage became deeper and wider and improvements in timbre & decay added up to a more musical presentation as opposed to analytical. Midrange magic with no fatigue. 

How does an amp contribute to imaging? 

Moreover, image and ’air’ can be quite delusional/artificial properties. Just go to a good concert hall and listen to a symphonic concert. Imaging there is usually far less precise than what you hear at home from your audio gear.

I would hope that at home, we have a much better seat and acoustics.  

With few exceptions, acoustics are typically terrible at live events. Concert halls are typically poor acoustically, especially if they have been built in the last 100 years.