Hello Eric Wallace,
RadSlider has three modes - numeric slider, items slider and ticks slider. In all three modes, the Value property stands for the value of the slider control itself. In case you have noticed, the Value of a slider item is of type String, whereas the Value property of the slider control is of type Decimal. That is why, it is simply not possible for the Value property of the slider control to return the value of the selected item. You are correct that it as an omission for our part, that we have not explained this in the documentation. I will log it in our ToDo list.
Regarding getting the value of the selected item, you can use the get_selectedValue method.
the Telerik team