Eventually, a bit like those sold-as-17in monitors with only 15.7in of visible area

No one ever claimed that there was 17" of viewable area. The tube itself is 17" in diagonal dimension, which is how tube manufacturers describe them, and that nomenclature is just carried through the monitor manufacturers. Just because the consumer hasn't bothered to investigate what is common knowledge among anyone with any passing familiarity with the industry isn't reason enough to claim fraud.

OTOH, drive manufacturer's GB claims, IMO, are intentionally fraudulent, as they are using a definition of terminology that is in opposition to everyone else's definition of the same terminology.