mojophone said:um ok call me stupid or gullible but you gotta be kidding me right? I mean people don't really lose height each day, do they? Got a link to tell me more ofthis phenomena
According to Wikpedia " A person's height also varies over the course of the day, by an average of 19 mm, gradually shrinking as the spine compresses over the course of a day, and stretching back out overnight (Tyrrell, et al. 1985)."
For those like me that don't use metric often 19mm is .75 inches
http://en.wikipedia.org/wiki/Human_height
I am not sure I buy that as a valid reason for not measuring once upon entry because I think there must be a bigger safety factor figured in for the height requirements to take into consideration mis-measurements and people getting by with larger shoes etc.
I think the reason WDW doesn't measure once is that its harder to fake your height multiple times throughout the day then it is to do it once. By taking your measurement more times, they are making it harder to cheat, and giving the CM's more chances of catching someone that is adding a cheat. I bet most of us could think of a way to add 2 inches to our height if we wanted if we only needed to be measured once.
Also by measuring once, some people may attempt to change ID bands and or bring their own in.
Edit: Maybe that is some of their reasoning but I can't believe its the only one.
You are good to go! No problems with thick soled shoes to fudge the height. Remove all hats too. Now, I wonder how many parents would stuff the kids pants with a couch cushion to improve height ? 
Its Disney World, dont sweat it, you will have a great time any way!!