A person unskilled in the arts of modern slang would take these phrases to be actual inquires into to the personal status of a friend or neighbor. And years ago, this would have indeed been the case.
But over the years, these greetings have been diluted to mere acknowledgements of the presence of others, if that. "How are you" means little more than "hi." And I despise this trend with a fiery passion.
When I ask an acquaintance “how they are doing,” I actually want to know if he is doing well, or if I should be worried about him. I am not simply saying hello. Similarly, when I ask a friend “what’s up,” I am not merely acknowledging his existence. I actually want to know if they are doing anything of interest, and whether I can help them in achieving their ends.
If I seek only to acknowledge your presence, I will do so with a nod or a wave or a "hi." But if I ask about you, I expect an answer. And I will answer your queries in similar fashion.