Kind of True.
With the advent of such great discount like
Free Dining and the 4/3 deal, at typically slower times of year, has really added to WDW's crowd numbers. September used to be, literally, almost empy, but now that is the height of free dining season. Now, don't get me wrong, the September crowds are lower than other times of the year, especially the incredibly crowded times like summer and holidays, but it's not as slow as it used to be.
Many schools, especially in the southeast, have fall breaks during the month of October and that, along with the huge popularity of Mickey's Not So Scarey Halloween party and pretty decent discounts, has really added to the crowd numbers. There are still some pretty slow time frames in January, you just have to fit them in between, New Year's, The Disney Marathon and the MLK holiday.
I think it comes down to the fact that Disney employs some pretty talented marketing geniuses and they are very good at what they do.