In 2007 was my first concert, at a peforming arts theatre, but I had a BAD seat. In 2008, it was at an events arena, but I was front row center!
I think you are getting at differences in what you see on DVD vs live. Like RetPgmr points out, you dont see the full orchestra and there are fewer choir members. I thought it was 3 women and 3 men in 2008, but could be wrong. But I think the more impressive differences are....
1. Mairead. She is a lot quicker in a live performance than you would think. Her jumps are also higher than they seem on a dvd. Plus, when I was front row center, I could hear when she leaps and lands. That was kind of strange yet very cool. You would never hear that on a dvd. Although she is small, she is built solid. Not masculine, but definately has some muscle on her. I would call her "fit", not "skinny" or "thin".
2. Eye contact. When you are close you get it. Now at times I wondered "Is she looking at me?" Perhaps, perhaps not. I thought I caught Alex's eye a few times, then read on a later thread somewhere that she often just looks to the back of the theatre, so it may have just seemed she was looking at me because she was right in front. Orla certainly looked my way, but also she could have been looking at the person behind me, or beside me, it can be hard to tell. But Orla certainly makes a lot of eye contact. Lisa scans the crowd and sometimes smiles at or acknowledges people. So does Mairead. Lynn seems a bit different with eye contact. In 2008 it seemed she did it, but at sort of angles. Not looking right at the person directly in front of her, but maybe 3-4 seats left or right.
3. Feedback. I guess you would call it. The guy next to me yelled "RAYYYY!!!!!!" when he came out for Dulaman. Ray seemed to be amused by it, got a big smile. They do seem to enjoy seeing the crowd enjoying themselves.