From the management/owner point of view, the company line is that if you announce to an employee his termination date in advance, then you'll be paying him from that point on for little or no production.
If a guy knows on August 1st that his last day of work will be August 15th, you're going to have a "lame duck" thing going on with this guy for the next two weeks.
Think about this issue in terms of the NFL and free agency too. Most people call the players all spoiled and rich, gauranteed contracts, over paid, etc.........But I don't hear alot about the teams and the GM's being creeps when a guy gets cut after a decade of "loyalty" to any one team. I can't tell you how many times I've thought "whatever happened to that guy", then find out he got cut a year or two ago and is now selling insurance or coaching a HS team in his home town.
I too have been "cut loose" w/o notice as well. That's not uncommon in construction, as it is such a fluid and "hot & cold" racket. You cannot gaurantee work, workload, etc............from one year to another. It's a highly cyclical industry. I keep that in mind as an employer......