But the most burning valet-related question of all for North Americans was surely: "Why don't these people know how to pronounce the word 'valet'? What's with this 'VAL it' nonsense?"
"VAL it" is indeed the first pronunciation still given in British dictionaries for this word, whereas on this side of the pond we say "VAL ay".
"Valet" came into French from the popular Latin vassellittus, a diminutive of vassus (servant), itself derived from a Celtic word and also at the origin of our word "vassal". In French, a valet was originally a young gentleman who was not yet a knight. By the 12th century, the word was already being used to mean a manservant, the only sense it had when it was borrowed into English in the 1300s. Judging by many spellings with two final t's, the final consonant seems to have been pronounced then, but in Scotland a t-less pronunciation, "vallie", also existed.
As far as I can gather, the word "valet" would have been familiar to Americans only through reading about Europe. Then valet parking was invented in the mid 1950s. When English has borrowed words from French since the Renaissance rather than before, the French pronunciation is usually preferred, especially in contexts implying prestige. I think that is why the more French-sounding "VAL ay" is used in North America for this word.
Another variant of the Old French valet was varlet. This underwent the same semantic evolution as "knave", which started out meaning "boy", then became "male servant" and eventually came to be a term of opprobrium, so that by the 1500s "varlet" meant, as the OED inimitably puts it:
A person of a low, mean, or knavish disposition; a knave, rogue, rascal.
Perhaps 15th-century valets/varlets were as nefarious as the evil Thomas at Downton!