yeah can defiantly understand why a lot of the more popular artists don't reply to every comment, its a little hard to keep up with things if you have limited amount of time though its always polite to get back to as much as you can and treat others with respect ^^
But then there are a select some who are legitimately nasty, using the people who look up to them the most to attack other artists, or be generally rude or uncaring to people, that's probably where this assumption manifested from in the first place.
I try to reply to all my watchers/ or watch them back so i can see their art and comment. Sometimes I don't feel like commenting and simply favorite the images. I don't get many people talking to me either aha, only some close friends but i have a good watcher base. Maybe its because they are intimidated / or have had bad experiences with artists who were arrogant and rude or some such which is understandable some of them can be quite rude but i can also see a point why popular artists are because I am always asked for trades or to give out free art when i don't have the time. I do try to be as polite as possible though, even if people are rude about it.
haha yeah I wouldn't worry about it too much though since all people judge in one way or another and end up surprised that the person they didn't know was actually a nice person. Offline I look like im constantly angry but that's just how my face is in a natural state when im actually a pretty sensitive and nice person so people tend to stay away from me aha. I'm used to it since i've had stuff like this happen all my life, once people realize how awesome you are more people will end up talking to ya.