in *my* opinion ppl tend to get their back up with wishing Wells because they're worried about being "judged" about the amount they can put in.
Honestly, I get my back up because I find it to be in exceptionally poor taste to tell your guests 'yeah, don't worry about a gift… we'll take your cash instead, thanks'. Just because something has become common place, and is accompanied by a sweet little poem, doesn't mean that it is not bad manners.