The way I see it:
1) The OP stating that it's impolite of those people to not respond isn't irrelevant. It actually goes to the core of the subject.
2) These people should (ideally) respond.
Why should they respond?
1) It's polite.
2) Internal reason: It's the logical thing to do: they post a thread containing a cry for help. Someone offers help... why not atleast try it? Honestly, if we were discussing this in an economical context there wouldn't even be a discussion
3) External reason: They should respond for the simple fact that they joined a forum like ALL. So many people on this forum deal with so many serious and sad issues on a daily basis. Many of them have noone to rely on, to trust, nobody to acknowledge them. Why would these kind of people, who are familiar with rejection, not acknowledge eachother? All it takes is a 'Thanks man
'... How can people ever truly solve/overcome these issues if even 'brothers in arms' don't stick together?
Besides, when you get a PM from someone, how can you tell that it didn't take a lot of courage/time/energy from that someone to just send it? It's like getting a thoughtful - but possibly sucky gift - from someone... do you acknowledge the thought/input or do you just throw it away in front of their eyes?
I (aswell as the OP) know that nobody owes anyone anything here in this context, but surely, wouldn't the forum be a better place if we all acted like is suggested by the OP? Can't we atleast acknowledge that? So why are there so many people rigorously trying to disagree with him? To me, that just feels like disagreeing just for the sake of disagreeing, and that saddens me.
But that's just how I see it.