Splenda is usually on the bottom of anything no matter how much of it is used because it is a high intensity sweetener. For example, if you look at a candy bar sweetened with splenda you will still see splenda on the bottom of the list. In the case of the pitas, they arent sweet, so there is probably just a touch to balance out the flavors.

Of course I have no problems with splenda and do eat products sweetened with it when I have a craving.