A potential implementation trouble with roaring crowds is that there is no one in WGT's HD photographs to make that roar. All the courses are glorious, deserted landscapes. All of our players are Robinson Crusoes, and even in multi-player games, you never catch a glimpse of your fellow players – only their golf balls or markers.
The roars and moans would be nice. We'd just have to accept the unrealistic part of it, that the crowds can't be seen anywhere. But there already are similar unrealistic features of this game that we've learned to accept as givens, such as trees never swaying in wind; immovable, non-reflective water surfaces; the physical absence of fellow players in multi-player games as described above, etc.
(It's much easier to oblige Mr. Boo's birds request, because we don't necessarily need to see birds to believe they are there.)