As an American who had the pleasure of spending a year in Germany as an exchange student, I love and appreciate this discussion

. It's good to acknowledge cultural differences and seek understanding.
I would argue that this is a case of a weak rule. English is odd, because, as James Nicoll put it:
"The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and riffle their pockets for new vocabulary."
We inherit a lot of words and techniques taken from other languages, along with a culture (in many English speaking countries) of adapting and changing things to suit local preferences. While there are firm rules, like Order Force (a positively Metal Name that refers to the exact order of types of adjectives describing something), there are also a lot of weaker rules that can often ignored or not even be known by most.
I think many of the examples here for is/are are situations where we might lean in one direction, but the other choice could work. Ambiguous, if you will

Saying "He are" would warrant a spanking, but saying "The staff is" or "The staff are" probably wouldn't ;)