Having spent a lot of time in a truck, I can tell you it's extremely difficult to cope on high-traffic roads. Most car drivers will crowd around you giving you no chance to change lanes, etc. Sometimes you have no choice but you just start creeping over and scare everyone out from around you. Obviously most truckers know what they're doing and they won't actually run you over -- it's bad for them, too.
When I'm out on the highway in a car and I see a truck ahead of me trying to get over into my lane, I'll most likely slow down to hold up the lane behind me and give them a quick headlights flash to they can get over. I'm sure the other cars hate me for it, but who cares.
The headlight flash is trucker code...if you do it for them they typically flash the trailer lights back...kinda like a salute and I can say they are typically appreciative (BTW...not a high beam flash but an off/on flash).
My father was a long haul truck driver (lower 48 states) for 35 years. 9mos/year on the road, moving furniture, loading his own truck as an owner operator...he was one of the good truckers with over 1 million safe driving miles...I cannot say they are all good drivers but a lot of them are. If they are an owner/operator all expenses are paid out of pocket (fuel, repairs, tires, food, taxes, etc.) so typically an owner operator is going to be more cautious than a driver who doesn't have to pay for damage.
On a side note there are certain trucking companies which hire mostly new drivers (Swift is an example) I typically watch out for those trucks.
Wish I could do an on/off flash. Darn automatic headlights can't turn off while driving. But most drivers know this and a quick brights flash is understood the same way.
Around the Twin Cities (Minneapolis/St.Paul) you get a lot of people in SUVs not taking into account the size and maneuvering of trucks. I have seen a couple try to pass from 3 cars back when the truck has already signaled a lane change. Then they get mad at the truck (lots of honking, cussing, etc.). It is especially annoying when you see the "look for motorcycles / bikes" bumper sticker on the vehicle acting like an idiot.
You are so right about the headlight flash, help the truck driver quite a bit.
The problem isn't on roads where you can turn left at all. It's a highway problem. And in the Northeast, it's standard for any three-lane road to have trucks in the right two lanes. Having trucks solely in the right lane leads to merging problems.
It seems like most of the folks who've commented with such authority ("there is no reason", indeed!) aren't really familiar with why the rules are as they are.
When I'm out on the highway in a car and I see a truck ahead of me trying to get over into my lane, I'll most likely slow down to hold up the lane behind me and give them a quick headlights flash to they can get over. I'm sure the other cars hate me for it, but who cares.