Computers aren't musicians, they are merely instruments, and we've gotten to the point that for an awful lot of things, those instruments played (programmed) by actual people can produce quite good results.
In the case of a pit orchestra, this just means one player could cover an entire multi-instrument "book" with a single EWI/EVI and laptop rather than actually physically switching instruments, but it would do nothing to alter the actual number of people required. Each person could still only play one part at a time. Electronics such as vocal harmonizers can be used to get around this to a degree, but those can be used with ordinary acoustic instruments as well (as the fact that they are VOCAL harmonizers would tend to imply).
If you've got the budget and space for a two-piece horn section, but have the means to make it sound like a four or six-piece horn section, who is being harmed by doing so? The number of people who would be up there playing doesn't change in either case.
DISCLAIMER: There's an EWI sitting within arm's reach of me as I type this. I may have a vested interest in proving it worthy for certain applications that AREN'T supposed to sound synthy.