The problem is a lot of people expect these fake hello's and how are you doing's. More than once in the workplace I have been confronted by people who want to know what my 'problem' is, and it comes from the fact that I don't say hello, how's your life every time I see people, unless we really are friendly enough that i really do care.
A "Hello" is a form of common courtesy. At its most basic level, it is the acknowledgement that an aquaintence or co-worker exists. A "Hello" cannot be faked since once given, it has served its purpose of (at the very least) acknowledging the existence of another. You say it, someone hears it, responds to you in kind. Thus, it is always real.
In the pet peeve I mentioned earlier, the thing that really got me upset was the fact that the guy completely pretended I was invisible. Not even just the lack of a "Thank You" for holding the door open for him, but the obnoxious jerk just kept right on walking like the bathroom door opened and held itself open. It was a blatant sign of disrespect on his part. The most basic kind too.
Add to that example the fact that many folks will give the Silent Treatment to someone with whom they are truly upset with. It's a subtle but clear way of letting someone know you don't appreciate what they did to you. Personally, I'll tell someone off who has upset me. But that's not the vast majority of folks out there. When you ignore someone, it's a way of disrespecting them without telling them to "F**K Off!"
Thing is, if you just don't want to be bothered saying "Hello" to a bunch of co-workers whom you'd never associate with if it wasn't for the job; they'll naturally assume it's because you don't like them, are upset with them, or that you're a jerk. They're your co-workers, and they're human-beings. They're not robots or computers. People tend to get very angry if you don't at the very least acknowledge that they even exist. Look at it from their point of view. How happy would you be if someone you knew walked right by you without even saying "Hello."