I think it's what we've historically been willing to settle for. If a yardage store started selling (or even giving away) yardsticks that were even 3 inches too long or too short, there'd be instant uproar. If carpet installers charged you for 10% more area than they really carpeted, there'd be threats of small claims court. But I think the market for measuring spoons is driven more by how nice they look and how well they "nest" into each other than even an expectation of 10% basic accuracy. For larger volumes, things are usually better...a 5-gallon bucket is pretty close to 5 gals and if you have 3 measuring cups, I'll bet they're within 5% of each other. Yet coffee pot vendors continue to think a cup of coffee is only 2/3 what an 8ounce cup really is.
I'd be curious what your local county's "weights & measures" applies to your local gas pumps. Call me liberal...I'm willing to pay taxes for consumer protections against outright fraud. But the pumps at my local gas station now pretty much say, "Joe has applied this pretty stamp, it's up to the user to verify accuracy." So what is this Bureau doing with my tax dollars? Do they really expect us to show up with empty milk jugs (which I trust to be a gallon) and measure out the gas and complain otherwise? How many gas station fires do we want as a society?
