Using my own field as an illustration, there are comics out there -- and no, I'm not going to mention any names -- that are hugely popular, with a wide, dedicated, and free-with-their-wallets audience ... but don't seem to be especially good strips. Most of them are at least decent, just nothing special, but for some reason they just turn people into glassy-eyed "looooove cooommmiiic" zombies.
Not all of the big strips are like this, by any stretch. Sinfest is both popular and a great strip, to pick one of the better ones at random. But there are several which, as far as I can tell, the only reason anybody reads the strip is because everybody else reads the strip! A few of these even go as far as to engage in what are often thought to be "kiss of death" bad practices that would have lower-level strips languishing to find even a single reader.
As a hard-working artist who is not blessed with this Midas Touch, I admit there's a certain amount of resentment there, but not as much as you might expect. I've met a few of the cartoonists behind these "Why the hell is this popular?" strips, and usually found them to be perfectly nice people that it's hard to nurse a grudge towards. What I usually find myself thinking instead is, "How can I get that kind of readership for my own strip?"
Of course, the problem with that question is that you can't. The fickle finger of fandom is like asking somebody out on a date: there are things you can do that are guaranteed to get "no," but there's nothing in the universe that can guarantee a "yes." Obviously, there are selloutey things I could do involving jiggly bits, fart jokes and so forth that would certainly get me more attention, but then it wouldn't be my strip any more, it would be an annoying thing that I spent all my time and effort on for no good reason ... which again doesn't solve the "how do I get it for my strip" question.
But it's still a question that bears thinking about. I am looking with serious intent at the idea of moving to professional or at least semi-professional status someday, and to do that, I'm going to need to really beef up my fanbase in a big way. Diversifying what I create (i.e., writing, print projects, working in more and different genres, and so on) is one way, but getting that SJ readership up as much as possible is an important factor.