Re: coasters, yeah, we never had that issue in my house growing up. We didn't have coffee or side tables so the only surfaces to set glasses on were the kitchen table or counters, which were fine without coasters. I only ever saw coasters at other people's houses and I would use one if told to or if I noticed others using them, but I wouldn't necessarily think of it on my own. I don't think coaster-using people are weird, by any means, but it's just never been a part of my lifestyle and I wouldn't think to ask for one somewhere.
It can be hard to know what is a reasonable assumption to make about other people's knowledge, and what isn't. There's a lot of grey areas in between the extremes. So I think the OP's multi-pronged approach is really good, since her original plan of assuming people knew what she wanted wasn't working.