Unfortunately,you are not ging to see many 8 piece bands in the casino lounges or shore venues ... but I have seen as many as 5 - 6 piece groups using back-up tracks ...
Those audiences want the music to sound like the original recording, hence 'dance clubs' only using DJs ... I've often said that the days of a band doing a 'pop' tune in their own style are looong gone ...
I have no issue with musicians enhancing their sound with backing tracks as long as they are not 'faking' a performace ...
As for the 'purists', I hope you 'keep on keepin' on' ... yours is a different audience from MOST of the arranger players on this board ... I, for one, would really dislike seeing that music/performance die ...

On chas' point about Miles, etc. ... I was attending an insurance agents convention one year and was excited by the fact that Dizzy was going to perform at the formal dinner ... Well, after dinner, Diz and his group took the stage and started playing ... the drone of voices in the room got louder and louder, to the point that after about 4 tunes Diz took the mic and said "apparently you folks would prefer to listen to each other, so GOODNIGHT", and they walked off the stage ... I was embarassed for the inconsiderate behavior of the people in the room ... After a while, my wife and I were out in the lobby and the fellow who booked Diz (who I knew pretty well) came walking out with Diz and we were introduced to him ... I apologized for what happened inside and he just shrugged and said something to the affect that his music isn't for everyone ... A class act ...
t.