You held factory workers to a very high standard, and I commend you for it. However, I believe even a factory worker is likely to learn new words through hearing them, either from his bosses, or from television. The amount of reading they do is bound to be small, and of common language (think US Today, not the "fancy" New Yorker or NYT).

As an interesting side-note, I cannot recall the American equivalent of British tabloids. Are there any ?

Don't underestimate the amount of reading done by factory workers. An average page turner fiction will use words like unfazed, and the person reading it will know what this word means, but will never use it in actual speech.

American tabloids? NY Post? I don't know, I'm not American.

There are many American tabloids. The National Enquirer is a staple at every checkout counter, along with others like The Globe, the Star, and Weekly World News.

Those are not the equivalent of British tabloids, they're just called by the same name.

As an aside, someone once pointed out to me that the National Enquirer is distinct from the other trashy tabloids. They never have the wacky "aliens stole my lunch" stories. They're focused on the gossip/celebrity domain and do a good job of it, as measured by: (1) they almost never lose a lawsuit, and thus (2) they rarely get sued. This person argued that the difference between the NE and "serious" papers was not one of accuracy or quality (making allowances for the lowbrow material) but rather in their willingness to pay for stories and photos.

I've tested this theory many times since while standing in queues at supermarkets, and I must say it checks out.