Which seems odd because every 4E campaign I'm part of (starting at level 1) is at least level 15 and over three years (and still going).
Certainly it can seem odd, compared to one's own experience. This merely demonstrates how one's own experience should not be taken as a stand-in for the experience of games as a whole.
Mind you, even giving the average doesn't really tell us as much as we want. We really need to know the standard deviation to also be able to characterize how long games last.
For example, at the moment I'm running a Deadlands campaign that's run for three years, and playing in a Star Wars Saga Edition game that's been running a couple of years. It would seem that my experience is similar to yours. Except, before those two games, I had a long stretch where I or another GM would offer to run a game, and a session or two would get played, and then life would intervene and things would fall apart. Each time that happens, my average campaign length drops precipitously, as the average of a 3-year game and a 0-year game is a 1.5 year game. So, my experience is at least vaguely consistent with the average...
But, is *that* the usual experience - the game goes for a long time, or not really at all? Maybe, or maybe not. I cannot say. A bunch of people here are saying that yes, having a campaign last a year or less is not odd for them, and I shouldn't discount them. The best we can say is that there are many different experiences, and in the past, at least, that averaged out to restarts rather more quickly than many expect.