Getting used to things may mean forming a better relatiotship with those. But it may mean muting one's sensitivity and emotions. The dead does not feel pain, so does the emotionally muted. (Nevertheless, it can be a useful strategy when no better option is there).
In the same venue I am not sure about what research found that the older are happier. It is higher satisfaciton with life. Meanig the person things better on his life. But are they indeed happier? or they just got used to a less good life? (Remember the research that as people grow they move form taking control on life, to inside control i.e. getting used to what there is, and conrolling the psych etc.)