I could go either way. On the one hand, he's in his own home, and using earphones means he isn't subjecting others to his stuff, which is polite. He may find it difficult to get "alone time" otherwise, especially if the household tends to be noisy--TVs on, people chatting, etc..
On the other hand, people can certainly go too far in isolating themselves from others in their household, to the point where other people feel ignored. And, I always found it kind of rude when my dad would walk into the living room to take a phone call, despite having phones all over the house, so that I had to turn the TV down--so if he's insisting that other people be quiet because he's listening to his stuff, I think that's not good.
Maybe the household can establish a "conversation time" when no one is paying attention to electronics but are just hanging out and chatting--meal times are often used for this. You could also think about modifying your communication style--if you have something you need to ask/say to him, maybe you could write a note and leave it for him, for example. (I'm imagining, "Add milk to the shopping list" or "Don't forget to get the oil changed.")