I think pretty much everybody is missing an important point of deadlines: money. If you are not done by the deadline you are dead. Management (with marketing) has a good idea of what will sell, fail to make the deadline and the product won't make money in the market and should be canceled early. This is the point of estimates: to decide early if the project is worth paying anyone to work on. (or course once you are part way in the project sunk costs become an issue)
Note a result of this is deadlines are not something you should come close to: a break-even project isn't worth your time to develop, so there should be plenty of slack in the schedule to cut into before hitting the point of no profit.
Note a result of this is deadlines are not something you should come close to: a break-even project isn't worth your time to develop, so there should be plenty of slack in the schedule to cut into before hitting the point of no profit.