Well. I think Londo did hear and did sincerely sympathize to a certain extent, but the full implications didn't penetrate. Because while the relationship Londo had with his family obviously wasn't without its troubles, the kinds of arguments he did have with his family - which can basically be boiled down to girls, curfew, and career, I think - were the sorts you can only have if you're a pretty secure - and pretty spoiled - adolescent. Have you ever heard a victim of genuine abuse or neglect complain that his parents don't "understand" him or won't let him do what he wants? I haven't, and in my personal life, I'm in a position to know.
To wit, just as selenak suggests in my favorite story, Lost in Translation, Londo's family didn't often tell him "no" early in life. And he never had to question, on a fundamental level, whether they even loved him. Thus, as he got older, he felt comfortable pushing the envelope a little bit because he had been conditioned to believe his charm would ultimately get him forgiveness - and perhaps a little something of what he wanted in the first place.
Granted, by the time we get to There All the Honor Lies, the spoiled brat in Londo has been told "no" more than once. But he hasn't learned the full lesson yet. He's still relatively deaf to the word, especially when he really, really wants something (*cough*G'Kar*cough*). And by the end of TAtHL, he really, really wants to make things right with Vir, because Vir is basically the only friend he has left at this point, and Londo is a man who needs friends like he needs air to breathe.
So. In typical fashion, Londo comes up with one of his heroically futile ideas: He's going to make things right between Vir and his family through sheer charisma. But here, also in typical fashion, he suffers from a failure of imagination. Because he was so doted upon by his own family, he can't conceive of a family without love. He hears "they just wanted me away" as "they don't understand me," and really, all he needs to do to fix that is arrange it so Vir's family can spend more quality time with the boy and thus get to know him better.
He was probably pretty shocked when he was confronted with the reality.