I took this question to mean two different things, but answered too fast on both accounts.
First: Do the players level to often in terms of RL time. This is largely dependant upon the game. People that play for one weekend (48 hours straight) every other month might say they level too quickly. Those who play weekly but only a few hours per session are more likely to say that it feels fine. However, I think this is much more a group dynamic perception.
Second: From a game mechanic perspective - is it right that the party levels after an average of 13 1/3 encounters. From this perspective I think the rate of advancement is absurd. To think that a person go into 13 1/3 combats and gain a level is rediculous in RL standards. For extended campaigns, it is precisely this fact that makes the orcs at level 1 seem so rediculously simple. After only 30 - 40 encounters orcs are just a non-issue unless they are classed.
For this reason, I am glad that in RL we advance when it feels appreopriate - not when the book says that you've "done enough." That's the way I'd rather have it.
The flip-side to this is the fact that we live in a disposable culture. When something is worn-out, broken, or just "not fun" any more we tend to toss it away. Thus, to keep us interested as a culture we must advance quickly because to not advance quickly would run the risk of 'reducing the fun' for most in our culture. I don't buy into that perception personally, but I know many do. The fun is getting to be omnipotent in totay's disposable culture. More often than not, the fun isn't in telling the story as much. It's in creating the ultimate character.