Often a big-name game will have a full orchestral score with one or two hours of music in total, and if one scrutinises the credits one can see that, yes, an orchestra (and often a choir) were the performers. But I have also heard it said that sometimes there is no orchestra, and the music is performed on a synthesiser using samples. If so, it suggests that with a big enough budget, one can get a much more realistic sound than comes out of, say, a play-through in Sibelius.
Yes, I get the feeling that 'midi'
will be, if it isn't already, a little more acceptable than some of our colleagues might give it credit for - never the same, of course, but passable..?