Quite right. In fact, I'd go further and suggest if you are not in the top half of your class after the first year, quit.

In my grad class at Rutgers, 3 are solidly on the tenure track (read: postdoc at good school), 3 did not finish (one is now in his 7'th year), the remainder are unlikely to get a tenured position.

I'm told that even at that other NJ school, only about 50% go on to get a tenure track job.