frankly, some guests at dinner may not be able to return the favour; if someone isn't equipped/monetarily or physically able to host in return, does that mean they have to stay home perpetually?

No, but you have to reciprocate in *some* fashion. If you can't host guests then you can at least initiate a phone call later on. (And I think most people do understand the difference between "Auntie Abigail has numerous obligations and also disabilities and cannot easily invite people to things" and "Jack from college would rather hang out with everybody else in the world but me, unless I'm paying".)