Like others said, it takes some empathy on the higher income side and it takes some modesty from the low income side to not be a mooch all the time.
I had a household income *MUCH* higher than several of my friends. Almost twice as skewed as the numbers in the OP. But it never affected us. When I went over I always brought the 12 pack of beer, usually bought the pizza, ect. It was never expected or assumed I would. I knew I was in a better situation so I gladly took care of that part. They opened their house to me, and we always had a great time and that was easily worth the cost of admission.
I'd never expect them to ante up tickets to an expensive concert or get pissy if they didn't buy baby gifts. Laughs and conversations are free. And that's what a lot of the expected contribution to a friendship is.
I enjoy reading about the psychology of different situations, and of course, every situation is really a two-edged sword, no matter how good (or bad) you have it. There's some interesting reading on Reddit here:
https://www.reddit.com/r/AskReddit/comments/2ir993/rich_people_of_reddit_what_does_it_feel_like/
https://www.reddit.com/r/AskReddit/comments/3hyfll/serious_rich_people_of_reddit_what_is_the_worst/
Reading through the comments of people who are wealthy, especially trust-fund kids, it seems like the best relationship is one where people don't expect you to pay at say dinner & will still offer to split the check, but of course will be covered. It's when people start expecting things in the relationship that you lose sight of the humanity because then it turns the rich friend into a dollar sign, i.e. just because you're rich means you should pay for everything when you go out.
I don't make six figures or anything, but I do alright. In contrast, one of my best friends isn't what I'd call poor, even though he makes maybe $20k a year, but he's kind of a freelance handyman & all of his hobbies are basically free (running, kayaking, biking, etc.), so his needs are few. I usually treat him out to lunch when we hang out because he helps me out a ton with stuff around the house, but he doesn't
expect me to pay all the time just because I have a solid full-time job, so it works out because he's not a moocher. I think generally, people don't like feeling taken advantage of or having expectations of sharing personal resources just because they have access to more of them than others...everyone wants to be treated like a human being.
And in the larger discussion of wealth, it really depends on what your personal needs are. I'm at the point where I'm making a decent living without having to kill myself with two or three jobs like I did in college. The best part is simply being able to go out to eat without having to check my bank account first...I can grab a meal out wherever or whenever I want. So for me, making a comfortable living is pretty much my definition of success & is more or less as high as I want to go financially. I don't really think I would have the discipline to be rich, because if I didn't have to work, I would turn into a couch potato for sure D: