I can understand adding the tip to the bill in this situation (there were 70 people there).

I'm not sure how much of the tip actually goes to the staff, but in this case I'm not sure it mattered. I have a feeling that the staff is well compensated (by tip or otherwise) as when we commented to the restaurant manager on duty that the staff were wonderful and she told us that they do everything possible to keep the staff happy so they stay working there.

It's too bad most restaurants aren't that way. Then tipping would be moot.