Pleats are never out, in my opinion. I prefer flat front dress slacks, but still prefer pleats on my suits. I don't know why it's difficult to find un-pleated pants for suits. If I were to hazzard a guess, I would suppose it's because the majority of folks prefer pleats on their suit pants, and when they are planning manufacturing in a RTW program, they go with what people want the vast majority of the time. This guess could be totally wrong.
I carry both Pleated and Non pleated. Flat front are pretty much OK for those that have flat rears. Any additionaly padding and you are gonna get into problems with who sees what. The reason that its so is that the pleated pants get an additional folded material somewhere in the seat which is folded into the waistband to create the pleat. The more pleats the more room in the seat. I wold probably get arrested if I tried a flat front,