contractor billing questions

I am almost finished with a kitchen renovation. Contractor is a long time acquaintance. We went over most contingencies and I was under the impression that labor would be covered by his estimate/agreement which was higher than everyone else (i used him because my cabinet guy and he are friends and they work together often and well). The deal stipulated that he would have to move a four inch waste pipe a few inches (burying it in a wall). Turns out, the way the work went, he didn't have to do that, so less work for him. So, should I expect a lower price? Probably not. But, it turns out he had to move a steam pipe that he (the contractor of 30 years who does "30 kitchens a year..." ) did not anticipate. Welll, he wants an extra $1200 for that work (he "usually charges $2500" for what I saw to be about 4 hours of work by him and 3-4 more hours of work by his worker. I've made my decision on this, but I'm curious what others think... I should also mention he's almost 2 weeks overdue at this point, and it will be a full 3 weeks late when finally done (I sure hope He lost about a day of labor, is overdue a few WEEKS, and thinks I should pay him an extra $1200 is how I look at it...