I worked for a moving company for many years.
First, when you pay for a move and use a National name like Allied, United, Mayflower, and pay for a local move at an hourly rate say 1 van and 2 men for $110.00 per hour, I can guarantee you, the majority of that money goes to the company, not the workers. Yes they make a pretty good wage, but like a waiter/waitress a tip is greatly appreciated to compensate their pay. They do not make "tons" of money.
In a move cross country, most of the drivers are now owner/operator's who have to hire their help from the local company at destination to deliver. The rate is determined by the local company, not how much they actually want to pay. I would definitely tip well if my goods came to me in very good condition and the driver and workers handled your items with care.
** just a side note, many of our drivers would have to give up jobs that delivered into Union shops because there was the possibility that they could lose money on the delivery. I know you are charged a lot to move, but trust me, some of the shops would have a minimum of 5 to 8 hours of pay no matter how long it took, with very high union rates.
While some workers make an excellent wage, the majority do not.
I would recommend that you tip if you want to and if you feel you received great service. If not, there is nothing wrong with not tipping, but please offer at least some water/soda and maybe a sandwich.
Hope your move went smoothly.