That said, I completely agree with the OP. If they ask, I'll always say "yes".
If they don't ask. That's not too cool IMO. Especially leaving a finger print or smudge on my crystal. I don't know how many times I'd have to ask for a cloth to polish my own crystal afterwards. The un-asked for, no-brainer advise givers are my least favorite. After playing with the pushers on my chronograph "Make sure you run the sub dial for seconds, using the big seconds hand drains the battery faster ."- "It was doing that before you started playing with it.""Could I have a watch crystal cloth please?"