I think the photo is just a symbol of all the ways that the wife has to cater to her MIL to avoid upsetting her, and she is just sick of it. I know, I know, interesting assumption. However, that's how it reads to me.
I'm trying to decide if I'd take the photo down or leave it up. My in laws are offended by body piercings (other than ears), alcohol, and many other things. However I was not about to take my navel piercing out when we all went swimming and it was visible. I would not even consider doing that and honestly it would never occur to me. They were probably also offended that I was in a two piece bathing suit now that I think about it.
Personally, I have a thing about people needing to like me for who I am or hey, don't like me at all, that's cool too. Your choice. But I'm not going to hide who I am for anybody. I'm not sure I'd have a nude photo on display personally, but if I did, I don't think I would have ever started taking it down.
As far as hosting, I definitely find out what people like and stock it. I already drink coffee but even if I didn't I'd keep a coffee maker in the house for guests. I see these things as hospitality, not changing who I am. Afterall, it's not like I'd prettend to drink coffee myself if I wasn't already a coffee drinker. I'm just offering it.