Maybe it's brilliantly done and special to the people giving the ovation. Just throwing that out there.
I think of standing ovations as just courteous. If it was a good concert, you should stand up to show your appreciation; you're about to stand up and leave anyway. If it's an incredible performance, then obviously the conductor/performer will be applauded long enough to take several bows (not just 2), and sometimes the soloist will give an encore performance. This is enough to differentiate between good and great performances.
If the audience doesn't stand up at all, it just feels awkward.
Do you know how much it sucks to not get a standing ovation?