As I understand it, it's pretty normal for children to imagine that they're the center of their own universe. Perhaps they don't think of themselves as television celebrities, but they nonetheless do tend to think that the world revolves around them. It is only as they get older and more mature that children begin to realize that, however interesting they may think their own lives are, other people tend to have other things to think about and be interested in. If a person doesn't grow up to realize that they aren't always going to be the center of attention, we rightly think that there is something wrong with them.
On the other hand, I wonder if maybe people don't need to imagine that they're the center of attention to at least some degree. While I would never advocate for out-and-out narcissism, and I'm certainly of the opinion that people should think of others before themselves, the fantasy of being the center of attention nonetheless does have some positive benefits. Perhaps I can illustrate the point through its antithesis, which Douglas Adams famously described via the "Total Perspective Vortex":
... when you are put into the Vortex you are given just one momentary glimpse of the entire unimaginable infinity of creation, and somewhere in it a tiny little marker, a microscopic dot on a microscopic dot, which says "you are here."The Total Perspective Vortex is described as the most horrific punishment imaginable, from which no being could survive. However, former galactic President (and all-around egotist) Zaphod Beeblebrox does survive his exposure to the Vortex, although there was admittedly a bit of a cheat. While Beeblebrox was in the Vortex, he was simultaneously in a computer-generated universe (and not actually the real one). This virtual universe having been created for Beeblebrox's benefit, the Vortex of that universe only told him the truth: that Beeblebrox was in fact the most important being in it, and thus the Vortex only confirmed what he already believed about himself. But, for most of us, the realization of just how insignificant we are in the grand scheme of things can be crippling. We actually need to be able to imagine ourselves as having some measure of importance in order to give our lives meaning.
I no longer have that fantasy about being a television star. Indeed, as I've grown up and seen the kinds of stresses that exist in the lives of such celebrities, to say nothing of the unwanted attention they receive, I know that I would actually not want such a life. Even so, I expect that blogging represents a modern form of the same concept, and I don't think I'm alone. We write as if anyone could be reading what we have to say, because in fact the potential is really there. Our words have the potential to reach a worldwide audience, and one never knows just who might be dropping in and when.
Indeed, I've read somewhere that the surest way to kill a blog is if the writer starts to write demonstrating a belief that no one is reading. If people read a blog that the writer doesn't think is important enough that people will read it, the readers will believe that impression... and they won't read it any more.
I try to balance out my fantasy of a worldwide audience with some measure of reality. I know what my daily stats are, and while I don't have the "hits" that many of my favorite bloggers have, I keep writing with the knowledge that none of them started out with thousands of visitors a day, either. We write because we believe that we can make a difference, and in acting on that belief, we make that belief come true.