Actually, I didn't explain that very well, did I. Really it is different for drinking glasses, and a pair of reading glasses, because you can have one glass that you drink out of, and a pair of glasses that you see through is only one. Maybe that can explain it better.

it's the same whether you are talking about drinking glasses or glasses that you wear to improve your eyesight. as everyone here has said, these glasses are nice, which can either mean a pair of reading glasses (one only), or drinking glasses, in which case, there are more than one. "It's a nice glass of water", or "they are nice glasses of water". Sorry, the English language sometimes uses the same word to describe different things.