Friedrich,
I think what you mean to say is that all the instruments in the pit are "amplified". There are many "acoustic" instruments in the pit...they all are except for the keyboards, bass and electric guitar, which are obviously...electronic.
The only reason they are all on mic is so that a good balance can be acheived. In some venues that is easier, in some that is harder. The Fox (St. Louis) is a huge cavern and the pit is huge and the front row of the audience is sooo far from the stage.
St. Louis is not one of the cities where we would pick up extra players for the larger orchestra, mainly strings, but also an extra woodwind. So you were getting "fake" strings", but the players are good and the orchestrations to Les Miz have always been great. I am sure it was a great show. I loved every minute of those two years!
Anyway, I probably shouldn't say this, but I was the MD/Conductor for the Les Miz tour for two years and was there in St. Louis on its last stop (before the final) in spring 2005. I only mention this for the people that might think..."What the hell is this guy talking about."
Ciao!