Replacing Pets?

I know someone (that used to go to my church) and I am still Facebook friends with her. 

She has a thing for Great Danes.  She had one that lived a pretty good long life (for a Great Dane), then about a week later, she had a new puppy (Maggie) to replace her.  Also a Great Dane.  She recently died and from what I can tell it was some kind of heart problem, she had surgery, while her owners were hiking through Europe (which they do about 2 or 3 times a year).  So it seems they were not even home when their dog died. 

She was only about 4 years old.  They got back from Europe and a couple of days later, they now have a new Great Dane pup (Molly). 

I am not saying that people shouldn't get a new pet after they lose one, in fact, I think it is great to give an animal a good home but I just don't understand how someone can move on so quickly.

I guess to people like that, a dog is a dog and not family.  I still tear up when I think about Thatcher and even after 14 years, I am STILL not ready for another dog.  I miss him so much and barely an hour passes when I don't think of him. 

How you you just replace a pet the next day after losing one?  It is something I just don't understand.