When paving material is first laid down, it has to be compacted (steamrolled). That's why, when you are told you are getting 2 1/2 inches, you need to know if that's 2 1/2 inches BEFORE or AFTER it gets squashed down to 1 inch, which often isn't enough. Ask your estimator. The answer you get should be AFTER compaction.
The same rules apply for almost every industry. There are paving outfits that roam around, promising cheap paving. They can get their prices down low by cutting corners. Using less material, not clarifying what "After Compaction" really means, paying their employees less money and using older equipment. The results aren't always what their clients pay for, but the results may only be discovered after a long, wet winter.
Everybody loves to save a buck, but when it ends up costing more in repairs or redo's later, it isn't much fun anymore.