I'm no doctor, but I broke my collarbone two years ago (badly) and had surgery.
Whilst I think it's true that having a plate in there would likely help Tony get back sooner, the wound created is quite large and would also need time to heal. Also the risk of getting an infection in that area post surgery is quite high, probably too high to warrant getting back a week or two earlier.
If it got infected he could be out even longer.
No surgery is a good thing I think, long term. It means the break isn't too bad.