It isn't necessary to rotate cigars. The important thing is for the humidity to be constant throughout the cigar, and this just takes time. If the cigars are placed in a humid environment for a short time, only the outer layers will be at the proper humidity while the inside won't. These differences within the cigar may account for the uneven burns.
AH! The light above my head just turned on. That makes sense. For some reason I've just had it in my mind that the purpose of a humidor is to keep the cigar from drying out and crumbling to dust under it's own weight. I don't know why it never occured to me that an evenly humidified cigar would cause a more even burn.

See, I just learned something.

Now, Is this the same reason why a cigar should be in a humidor for a period of time for the flavors to become optimal? Is that related to even humidity or is that purly an effect of the different oils in the tobacco mixing over time?