I see nothing wrong with not knowing that. The people that don't know standard lumber dimensions are not stupid. They probably know a ton of stuff I don't know, like how to keep score in tennis or what it's like to shovel snow.
To me this seems more of an opportunity to educate than a need to mock people who never had to build a deck before. I find the process of turning trees into studs and posts fascinating. It seems like an opportunity for watching a YouTube videos that shows how there are a lot of steps after sawing a board into a 4"x4" post before it turns up at Home Depot, mainly it gets dried, which shrinks it, and then it gets planed on all 4 sides, which gets it down to the final standard dimension.
I started an informal Twitter poll to see how many people think a 4x4 is really 4x4. More than I would've thought. 75% of respondents knew 4x4 was nominal and not the actual size. 25% really thought it was 4 inches square. (n=44, which is a lot more than the 18 questioned in the store for the original story, and they got 1/3 not knowing vs my 1/4)
I also got some comments from people saying it's not the same where they are, outside the US. I did some digging to see what people call dimensional lumber in other countries, particularly ones that use the metric system. They still call a stud a 2x4 or maybe a 4x2. Wikipedia says that they say timber instead of lumber for building materials, but I haven't been able to confirm this.You buy a standard 8' long square post that is called a 4x4. What are the width and depth? (pretend it is dry)— Barbara Tomlinson (@beachton) June 26, 2017
I found anecdotal evidence that Norwegians have their own lumber dimensions, 95 mm for a 4x4, which is about 3 3/4", 1/4" bigger than the American version. They dimension drawings and give the specs in mm. This used to be true for the US as well. When I did AutoCAD work for the Army Corps of Engineers in the '90s they required all architectural plans to be dimensioned in mm. According to David Luke at Merrick this is no longer the case. They dropped that requirement around 2005.
But even though the actual size may vary my research shows that all around they world they still say "two by four" to refer to a standard piece of framing lumber. (Here's an interesting pdf about Japan where they have their own standard stick frame construction but "2x4" is still part of the name. It's based on a 3'x6' panel convention vs our 4'x8' version. This sounds good to me. I might not have such an aversion to doing anything with sheet goods if they were that small. Apparently 3'x6' is the standard size of a traditional tatami mat.)
I haven't come up with any good ideas for better names for 4x4s, 2x4s, etc. It doesn't really make sense to rename them based on a round metric number since everything else is still in inches and feet. I would support a sudden change to metric though. I could learn to say 90x90 and 40x90 as easily as I converted myself from °F to °C. (I just flipped the switch on my thermostats and weather app and learned that 25°C is a good nominal summer air conditioner setting. I think of 15°C as a summer night in the UK and anything less than that I call cold.)
Anyway, back to the lawsuit. Home Depot clearly states the actual size of all their lumber on their website. And if you're in the store you can see what size it is with your actual eyeballs and get a tape measure out of your purse and measure it if you want to.
Here's the description of a Pressure Treated 4x4x8 (which they seem to have measured soaking wet). I don't think anything will come from this except that a lot of people may learn what nominal and actual mean.
Interestingly you can also learn lots of other information about lumber from the Home Depot website by reading the reviews. Yes, a 4x4 is going to twist like a bitch when it dries. Prepare yourself. I learned to install my deck railing posts long and brace them diagonally until they dried in place. Then I took off the braces and cut them to length and finished the railing.
Good luck to all the DIYers out there. It's hard enough with the names of the wood not matching the measurement without people in the trades mocking you for not knowing it. But getting mad in the Home Depot reviews because wood acts like wood is pretty mean too. Acting all butthurt when carpentry turns out to be a lot harder than it looks on HGTV is insulting to people who do this for a living so I sort of get why they turn so mean.